Document:

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                                                                   Exhibit 10.35
                                                                   -------------

Portions of this exhibit were omitted and filed separately with the Securities
and Exchange Commission pursuant to an application for confidential treatment
filed with the Commission pursuant to Rule 24b-2 under the Securities Exchange
Act of 1934.  Such portions are marked by asterisks.

                    COPROMOTION AND CODEVELOPMENT AGREEMENT

This Copromotion and Codevelopment Agreement (together with all Exhibits, this
"Agreement"), effective as of September 9, 2001, is made by and between
ViroPharma Incorporated, a Delaware corporation (hereinafter "ViroPharma"), with
primary offices located at 405 Eagleview Boulevard, Exton, PA 19341, and Aventis
Pharmaceuticals Inc., a Delaware corporation (hereinafter "Aventis"), with
offices located at Route 202-206, P.O. Box 6800, Bridgewater, New Jersey 08807.
ViroPharma and Aventis may be referred to herein as a "Party" or collectively as
"Parties."

WHEREAS, ViroPharma has certain exclusive rights under the SaSy Patents and the
ViroPharma Patents and the Trademarks in the Territory (as each is hereinafter
defined); and

WHEREAS, ViroPharma intends to seek regulatory approval to market, distribute
and sell VP Products (as hereinafter defined) in the Territory; and

WHEREAS, ViroPharma and Aventis each desire to collaborate with the other in the
development and marketing of VP Products in the Territory pursuant to the terms
set forth in this Agreement.

NOW, THEREFORE, for and in consideration of the foregoing and the
representations, covenants and agreements contained herein, ViroPharma and
Aventis, intending to be legally bound, hereby agree as follows:

1.   DEFINITIONS.

     1.1  "13D Group" means any group of Persons formed for the purpose of
          acquiring, holding, voting or disposing of Voting Securities which
          would be required under Section 13(d) of the Exchange Act and the
          rules and regulations thereunder to file a statement on Schedule 13D
          with the SEC as a "person" within the meaning of Section 13(d)(3) of
          the Exchange Act. Ownership of Voting Securities shall be determined
          in accordance with Rule l3d-3 of the Exchange Act as currently in
          effect.

     1.2  "Additional Indications" means either or both of:

          1.2.1  Prevention of VRI in patients with asthma and reduction in
                 associated lower respiratory tract morbidity (the "Asthma
                 Indication"); or
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          1.2.2  Prevention of VRI in patients with chronic obstructive
                 pulmonary disease and reduction in associated lower respiratory
                 tract morbidity (the "COPD Indication").

     1.3  "Adverse Drug Experience" means any of: an "adverse drug experience,"
          a "life-threatening adverse drug experience," a "serious adverse drug
          experience," or an "unexpected adverse drug experience," as those
          terms are defined at either 21 C.F.R. (S) 312.32 or 21 C.F.R.
                               ------
          (S) 314.80.

     1.4  "Affiliate" means any person or entity that directly or indirectly
          controls or is controlled by or is under common control with
          ViroPharma or Aventis, as the case may be, but only for so long as
          said control shall continue. As used herein the term "control" means:

          1.4.1  the direct or indirect ownership of over fifty percent (50%) of
                 the outstanding voting securities of an entity or person (or,
                 such lesser percentage which is the maximum allowed to be owned
                 by a foreign corporation in a particular jurisdiction), or

          1.4.2  the right to receive over fifty percent (50%) of the profits or
                 earnings of an entity or person (or, such lesser percentage
                 which is the maximum allowed to be owned by a foreign
                 corporation in a particular jurisdiction), or

          1.4.3  such other relationship as in fact gives such individual or
                 entity the power or ability to control the management, business
                 and affairs of an entity or person.

     1.5  "Assigned Sales Force Effort" shall mean the number and type of PDEs
          to be performed by a Party for a VP Product in the Territory in each
          month during any Calendar Quarter, as assigned by the Marketing
          Subcommittee under the then applicable Commercialization Plan and
          Budget and in accordance with Section 5.4.

     1.6  "Aventis Competitor" means:

          1.6.1  an entity which, together with its Affiliates is among the top
                 twenty (20) pharmaceutical products companies in North America
                 based on annual revenues from North American sales of
                 pharmaceutical products in the Calendar Year immediately
                 preceding the Change of Control of ViroPharma, as reported by
                 IMS Health Incorporated;

          1.6.2  an entity that sells a pharmaceutical product which is a direct
                 competitor of one of Aventis' top (15) pharmaceutical products
                 based on annual global revenues from such pharmaceutical
                 product, provided that such competing product has achieved a
                 North American market share of at least seven and one-half
                 percent (7.5%) for the Calendar Year immediately preceding the
                 Change of Control of ViroPharma based on total
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                 prescription sales, as reported in the corresponding IMS ATC II
                 or III category; or

          1.6.3  an entity that is an Affiliate of one of the foregoing.

     1.7  "Aventis Interest" means Aventis' interest in both its rights and
          obligations pursuant to this Agreement, including, without limitation,
          with respect to, (a) the prescription market for VP Product, taking
          into account pending NDA filings and any ongoing development
          activities for any VP Product, in each case considering the likelihood
          of success, actual and the likelihood of potential competition from
          generic drugs, the likelihood that any Regulatory Authority would
          require that any VP Products be sold without prescription labeling
          restrictions, and the likelihood that actual or effective exclusivity
          could be maintained or extended as a result of the issuance of patents
          under then-pending additional patent applications, pursuant to
          litigation to assert pre-existing rights, or in any other manner
          consistent with Laws, and in each case considering actual and
          potential competition from any Third Party prescription or over-the-
          counter pharmaceutical product, (b) any VP Product Exclusivity Unit
          that a Regulatory Authority required to be sold without prescription
          labeling restrictions before the expiration of the VP Product
          Exclusivity Period for such VP Product Exclusivity Unit, as described
          in Section 2.7.2, and (c) any VP Exclusivity Unit for which there was
          a Voluntary OTC Switch, as described in Section 2.7.3, but excluding:

          1.7.1  the effect of ViroPharma's exercise of its right under Section
                 2.7.5(b);

          1.7.2  any element of value arising from the accomplishment or
                 expectation of any Change in Control, including, without
                 limitation, any Patents or other intellectual property rights
                 owned or Controlled by any Third Party involved in such Change
                 of Control before the completion of such Change of Control; and

          1.7.3  any economic benefits or rights accruing to Aventis from the
                 Effective Date to the date immediately preceding the date of
                 any closing of a purchase and sale of the Aventis Interest
                 pursuant to either of Section 2.7.5 or 12.5 (including, without
                 limitation, the right to receive payments pursuant to this
                 Agreement).

     1.8  "Aventis Know-How" means all know-how, processes, materials,
          information, data and analyses including copyright and trade secret
          related thereto owned or Controlled by Aventis to the extent necessary
          to develop, or permit the use, sale, or offering for sale of VP
          Products.

     1.9  "Aventis Logo" means the Aventis name logo set forth on Exhibit 1.9,
          and all copyright and trademarks relating thereto.

     1.10 "Aventis Product Target Prescribers" means the list of approximately
          ****** (******) prescribing physicians developed by Aventis and
          provided to ViroPharma to whom the Detailing of Aventis Product(s)
          shall be performed.
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     1.11  "Aventis Technology" means the Aventis Know-How and the Aventis Logo.

     1.12  "Aventis Trade Policy" means the Aventis policy governing the sale
           and return of products, which is attached to this Agreement as
           Exhibit 1.12, without giving effect to the provision in such policy
           permitting Aventis unilaterally to alter such policy to the extent
           such alteration would be material, but including any material changes
           to such policy affecting the treatment of VP Product returns and
           refunds approved in advance by the JSC.

     1.13  "Beneficial Ownership" of securities means having "beneficial
           ownership" of such securities (as determined pursuant to Rule l3d-3
           under the Exchange Act), including pursuant to any agreement,
           arrangement or understanding, whether or not in writing.

     1.14  "Calendar Quarter" means each or any of the three month periods
           ending March 31, June 30, September 30 and December 31, except that
           the first Calendar Quarter shall be the period from the Effective
           Date until the earliest of the immediately following March 31, June
           30, September 30 and December 31.

     1.15  "Calendar Year" means each twelve month period of the Agreement
           ending on December 31, except that the first Calendar Year shall be
           the period from the Effective Date until the immediately following
           December 31.

     1.16  "Call" means a face-to-face contact (and, subject to the approval of
           the JSC, a live video presentation) of either a ViroPharma or Aventis
           sales representative, including permitted representatives of contract
           sales organizations (to the extent permitted under Section 5.5.3),
           with medical professional(s) with prescribing authority during which
           Details are performed.

     1.17  "Canada" means Canada and its territories, commonwealths and
           possessions.

     1.18  "Change of Control" means an event where:

           1.18.1  any Person, group of Persons acting jointly on the basis of
                   an agreement or understanding with each other relating to the
                   exercise of voting rights, or 13D Group in each case not
                   including any Affiliates of either Party, acquires (whether
                   by direct acquisition, merger, consolidation or similar
                   transaction) directly or indirectly, control of more than
                   fifty percent (50%) of the Total Voting Power of all Voting
                   Securities of ViroPharma or any of its Affiliates that is
                   either a sublicensee or assignee of all or substantially all
                   of ViroPharma's rights or obligations under this Agreement or
                   of Aventis S.A. or Aventis or any of their respective
                   Affiliates that is either a sublicensee or assignee of all or
                   substantially all of Aventis' rights or obligations under
                   this Agreement, as the case may be;

           1.18.2  Aventis S.A. or Aventis, or ViroPharma, as the case may be,
                   directly or indirectly, sells or otherwise transfers to any
                   Person or group of Persons
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                   who are not Affiliates of such Party, all or substantially
                   all of its properties and assets.

           1.18.3  In the case of ViroPharma, any other transaction within the
                   meaning of a "change in control" pursuant to the SaSy
                   Agreement.

     1.19  "Collaboration Royalties" means all royalties and other amounts paid
           to Third Parties for patent or technology licenses that the JSC
           agrees are necessary or desirable in order to develop, make or have
           made, use, sell, or offer for sale in the Territory, or import into
           the Territory any VP Product, but shall not include SaSy Royalties or
           other royalties and amounts paid by ViroPharma to Third Parties
           pursuant to Section 10.2.5(c).

     1.20  "Combination Product" means a product composed of VP Compound or VP
           Product and at least one other therapeutically or prophylactically
           active pharmaceutical ingredient that is not a VP Compound or VP
           Product.

     1.21  "Commercialization Expenses" means the following:

           1.21.1  Detail Cost of VP Product, but in no event shall
                   Commercialization Expenses include the costs of training each
                   Party's respective sales force dedicated to promoting VP
                   Product, or the costs of sales meetings;

           1.21.2  the Cost of Goods sold;

           1.21.3  the cost of obsolete VP Compound, the costs to dispose of
                   obsolete VP Compound, and the cost to dispose of obsolete VP
                   Product, to the extent such costs are not allocated to
                   ViroPharma alone under this Agreement;

           1.21.4  Cost of Goods of Samples;

           1.21.5  Cost of Goods of VP Product used in any Phase 3b Studies or
                   Phase 4 Studies;

           1.21.6  SaSy Royalties;

           1.21.7  Collaboration Royalties;

           1.21.8  costs for the creation, review, production and distribution
                   of Promotional Materials;

           1.21.9  costs for promotional and educational meetings;

           1.21.10 costs for medical and professional education;

           1.21.11 costs for opinion leader and advocacy development;

           1.21.12 costs for public relations related to a VP Product;
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           1.21.13 costs for the development, conduct and analysis of market
                   research studies and data;

           1.21.14 costs for activities related to obtaining reimbursement from
                   payors;

           1.21.15 costs for distribution of Samples to each Party's
                   distribution center (but not including the costs of
                   distribution of Samples from such distribution centers to
                   each Party's sales representatives, the tracking and auditing
                   of Samples after receipt at each Party's distribution center,
                   the costs of Sample receipt forms and other costs of
                   compliance with the PDMA);

          1.21.16  costs for medical affairs services for VP Product as
                   described in Section 7.7;

          1.21.17  costs for Phase 3b Studies and Phase 4 Studies;

          1.21.18  costs for handling orders and booking sales pursuant to
                   Section 5.10;

          1.21.19  costs for launch meetings held jointly by the Parties,
                   excluding the lodging and travel costs of each Party's
                   attendees at such launch meetings;

          1.21.20  costs incurred in connection with post-approval regulatory
                   matters other than post-approval labeling enhancement;

          1.21.21  a reasonable allowance for doubtful accounts receivable;

          1.21.22  costs for Distribution of VP Product;

          1.21.23  freight, insurance and other transportation charges for VP
                   Product to the extent not included in the invoice price;

          1.21.24  any other costs identified as Commercialization Expenses in
                   this Agreement;

          1.21.25  any other costs approved in writing by the Marketing
                   Subcommittee before such cost is charged to a Party's
                   Commercialization Account;

          incurred for a VP Product after the Effective Date of this Agreement,
          and actually paid to Third Parties or accrued therefor, net of any
          credits or refunds made on account thereof by such Third Party, as
          provided for in an approved Commercialization Plan and Budget, or as
          otherwise approved in writing by the JSC before such cost is charged
          to a Party's Commercialization Account. "Commercialization Expenses"
          shall not include any internal costs of commercialization activities
          unless the JSC has specifically authorized the charging of such
          internal costs to a Party's Commercialization Account in writing
          before such cost is charged to a Party's Commercialization Account.
          Notwithstanding anything to the contrary in this Section 1.21, the
          internal costs associated with Detail Costs of VP Product, and any
          amounts deducted from gross
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          sales to obtain Net Sales as set forth in Section 1.61 shall not be
          included in "Commercialization Expenses," and in no event shall a
          single expense be charged more than once as a Commercialization
          Expense.

     1.22 "Commercialization Plan and Budget" means the Commercialization Plans
          and Budgets described in Section 5.3.

     1.23 "Compound" means a chemical compound or substance together with all
          complexes, mixtures and other combinations, prodrugs, metabolites,
          enantiomers, salt forms, racemates, and isomers thereof.

     1.24 "Confidential Information" means all secret, confidential or
          proprietary information or data, whether provided in written, oral,
          graphic, video, computer or other form, provided by one Party (the
          "Disclosing Party") to the other Party (the "Receiving Party")
          pursuant to this Agreement or the Mutual Non-Disclosure Agreement
          between the Parties dated March 1, 2001, or generated pursuant to this
          Agreement, including but not limited to information relating to the
          Disclosing Party's existing or proposed research, development efforts,
          patent applications, business or products, the terms of this
          Agreement, the terms of the SaSy Agreement, and any other materials
          that have not been made available by the Disclosing Party to the
          general public. Notwithstanding the foregoing sentence, Confidential
          Information shall not include any information or materials that:

          1.24.1 were already known to the Receiving Party or its Affiliates
                 (other than under an obligation of confidentiality), at the
                 time of disclosure by the Disclosing Party to the extent such
                 Receiving Party has documentary evidence to that effect;

          1.24.2 were generally available to the public or otherwise part of the
                 public domain at the time of its disclosure to the Receiving
                 Party or its Affiliates;

          1.24.3 became generally available to the public or otherwise part of
                 the public domain after its disclosure or development, as the
                 case may be, and other than through any act or omission of a
                 Party or its Affiliates in breach of such Party's or such
                 Party's Affiliates confidentiality obligations under this
                 Agreement;

          1.24.4 were disclosed to a Party or its Affiliates, other than under
                 an obligation of confidentiality, by a Third Party who had no
                 obligation to the Disclosing Party not to disclose such
                 information to others; or

          1.24.5 were independently discovered or developed by or on behalf of
                 the Receiving Party or its Affiliates without the use of the
                 Confidential Information belonging to the other Party and the
                 Receiving Party has documentary evidence to that effect.

     1.25 "Control" or "Controlled" means with respect to any (a) item of
          information, or (b) intellectual property right, the possession
          (whether by ownership or license,
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          other than pursuant to this Agreement) by a Party of the ability to
          grant to the other Party access and/or a license to such item or right
          without violating the terms of any agreement or other arrangements
          with any Third Party existing before or after the Effective Date.

     1.26 "Cost of Goods" means, the total cost to produce VP Product in final
          form for sale or for use as a Sample actually paid to Third Parties,
          including, but not limited to, the costs of bulk material or VP
          Compound, the cost of micronization and other processing, the cost of
          excipients, the cost to manufacture final product, the cost of fill
          and finish, quality control, labeling, packaging and shipping to a
          Party or its Affiliate or contractor, and the cost of storage.
          Notwithstanding the foregoing, any payments made by Aventis for
          Finished VP Products to ViroPharma or to a Product Supplier of
          Finished VP Product shall be deemed a "Cost of Goods" and shall be
          charged to Aventis' Commercialization Account when sold, and
          ViroPharma shall not charge its costs or payments to Third Parties to
          produce such Finished VP Products to its Commercialization Account. If
          Aventis manufactures VP Compounds or VP Products, then the definition
          of "Cost of Goods" shall be revised as mutually agreed to by the
          Parties.

     1.27 "Curable ViroPharma Breach" means the breach by ViroPharma of any
          material representation, warranty, covenant or agreement set forth
          herein, that is curable by either Party hereunder, and that remains
          uncured by ViroPharma following the cure period(s) set forth in
          Section 13.7.1.

     1.28 "Detail" means a face-to-face contact (and, subject to the approval of
          the JSC, a live video presentation) of either a ViroPharma or Aventis
          sales representative, including permitted representatives of contract
          sales organizations (to the extent permitted under Section 5.5.3),
          with medical professional(s) with prescribing authority, during which
          a complete VP Product or Aventis Product presentation, as defined from
          time to time by the Marketing Subcommittee or Aventis, as applicable,
          is communicated, but may include leaving with such medical
          professional such promotional materials as are designated by the
          Marketing Subcommittee or Aventis, as applicable and product samples
          in quantities designated by the Marketing Subcommittee or Aventis, as
          applicable. In each case a Detail shall be as measured by each Party's
          internal recording of such activity consistent with the methodology
          established by the Marketing Subcommittee pursuant to Section 5.7.1,
          or by Aventis, as applicable. When used as a verb, "Detail" means to
          perform a Detail.

     1.29 "Detail Cost of Aventis Product(s)" means, unless otherwise agreed to
          by the JSC:

          1.29.1 during such time as ViroPharma is promoting and Detailing only
                 Aventis Products as a contract sales organization on behalf of
                 Aventis (i.e., prior to the Launch Date), $****** per Call,
                 which Call shall include one Primary and one Secondary Detail
                 of Aventis Products; and
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          1.29.2  during such time as ViroPharma is promoting and Detailing any
                  VP Product and an Aventis Product, $****** per Secondary
                             ---
                  Detail of Aventis Product (where, for the sake of clarity,
                  this amount was calculated on the basis of a $****** FTE Rate,
                  for a sales representative performing ****** calls per year,
                  and allocating ******% to the Secondary Detail);

          in each case adjusted annually for inflation by the Finance
          Subcommittee beginning with respect to Calendar Year 2003 to an amount
          equal to such amount listed above in this Section 1.29, multiplied by
          the U.S. Department of Labor's Consumer Price Index for All Urban
          Consumers (CPI-U) ("CPI") at the time of the adjustment ("CPI
          \\New\\"), divided by the CPI on January 1, 2002 ("CPI\\Base\\").
          Represented arithmetically, the new Detail Cost shall be:

                 Old Detail Cost  x  (CPI\\New\\/CPI\\Base\\).

     1.30 "Detail Cost of VP Product" means, unless otherwise agreed to by the
          JSC:

          1.30.1 in the case of ViroPharma, during such time as ViroPharma is
                 promoting and Detailing one or more VP Products, $****** per
                 Primary Detail and $****** per Secondary Detail of VP Product
                 (where, for the sake of clarity, these amounts were calculated
                 on the basis of a $****** FTE Rate, for a sales representative
                 performing ****** calls per year, and allocating ******% to
                 Primary and ******% to Secondary Detail); and

          1.30.2 in the case of Aventis, $****** per Primary Detail and $******
                 per Secondary Detail of VP Product (where, for the sake of
                 clarity, these amounts were calculated on the basis of a
                 $****** FTE Rate, for a sales representative performing ******
                 calls per year, and allocating ******% to Primary and ******%
                 to Secondary Detail);

          in each case adjusted annually for inflation by the Finance
          Subcommittee beginning with respect to Calendar Year 2003 to an amount
          equal to such amount listed above in this Section 1.30, multiplied by
          the U.S. Department of Labor's Consumer Price Index for All Urban
          Consumers (CPI-U) ("CPI") at the time of the adjustment ("CPI
          \\New\\"), divided by the CPI on January 1, 2002 ("CPI\\Base\\").
          Represented arithmetically, the new Detail Cost shall be:

                 Old Detail Cost  x  (CPI\\New\\/CPI\\Base\\).

     1.31 "Development Expenses" means the actual cost of each of the following
          for VP Product incurred on or after the Effective Date of this
          Agreement, in each case to the extent provided for in an approved
          Development Plan and Budget, or otherwise approved in writing by the
          JSC before such cost is charged to a Party's Development Account:

          1.31.1 all actual payments made to Third Parties or accrued therefor,
                 and all Development FTE Costs associated with:
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                 (A)  any preclinical or clinical study of VP Product for use in
                      the Field, including without limitation Phase 3a Studies,
                      but excluding any Phase 3b Studies or Phase 4 Studies,

                 (B)  obtaining VP Product used in any preclinical or clinical
                      study of VP Product for use in the Field, including
                      without limitation Phase 3a Studies, but excluding any
                      Phase 3b Studies or Phase 4 Studies,

                 (C)  regulatory filings and other regulatory expenses
                      associated with any preclinical or clinical study of VP
                      Product for use in the Field, including without limitation
                      Phase 3a Studies, but excluding any Phase 3b Studies or
                      Phase 4 Studies;

                 (D)  the preparation of an NDA, and for NDA filing costs and
                      fees;

                 (E)  all post-approval expenses resulting from labeling
                      enhancements of VP Products;

                 (F)  adverse experience reporting pursuant to Section 7.4;

                 (G)  any clinical study to be performed which is requested by
                      the FDA as a condition of approval of a VP Product;

                 (H)  any other costs identified as Development Expenses in this
                      Agreement;

                 (I)  any other activities provided for in the Development Plan
                      and Budget or approved in writing by the Development
                      Subcommittee or the JSC before such cost is charged to a
                      Party's Development Account; and

          1.31.2 the Cost of Goods of any VP Product used in any preclinical or
                 clinical study of VP Product for use in the Field, including
                 without limitation Phase 3a Studies, but excluding any Phase 3b
                 Studies or Phase 4 Studies.

          In no event shall a single expense be charged more than once as a
          Development Expense.

     1.32 "Development FTE Costs" means the product of: (a) the respective
          Party's Development FTE Rate, and (b) the actual number of FTEs, not
          to include administrative support personnel, utilized by such Party in
          performing activities in accordance with the Development Plan and
          Budget, or for other activities, but only to the extent the JSC has
          specifically authorized such other activities in writing before the
          Development FTE Costs of such other activities are charged to a
          Party's Development Account, measured in accordance with a tracking
          system substantially similar to that in effect on the Effective Date,
          or as otherwise approved by the FSC.
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     1.33    "Development FTE Rate of ViroPharma" means the FTE rate of ******
             U.S. dollars (U.S. $******) per person per year, adjusted annually
             for inflation by the Finance Subcommittee beginning in Calendar
             Year 2003 to an amount equal to the product of such amount, and the
             U.S. Department of Labor's Consumer Price Index for All Urban
             Consumers (CPI-U) ("CPI") at the time of the adjustment
             ("CPI\\New\\") divided by the CPI on January 1, 2002
             ("CPI\\Base\\"). Represented arithmetically, the new Development
             FTE Rate shall be:

            Old Development FTE Rate  x  (CPI\\New\\/CPI\\Base\\).

     1.34    "Development FTE Rate of Aventis" means the FTE rate amount, per
             person per year, as determined in writing by the JSC for the
             respective development activity to be performed by Aventis, as
             adjusted annually for inflation by the Finance Subcommittee to an
             amount equal to the product of such amount, and the U.S. Department
             of Labor's Consumer Price Index for All Urban Consumers (CPI-U)
             ("CPI") at the time of the adjustment ("CPI\\New\\") divided by the
             CPI on the date such FTE rate amount is first selected
             ("CPI\\Base\\"). Represented arithmetically, the new Development
             FTE Rate shall be:

            Old Development FTE Rate  x  (CPI\\New\\/CPI\\Base\\).

     1.35    "Development Plan and Budget" means the Initial Development Plan
             and Budget and each of the subsequent plans and budgets described
             in Section 4.4. 1.36 "Development Subcommittee" or "DSC" means the
             committee described in Section 3.5.

     1.37    "Distribution" of Finished VP Product means shipping, storing,
             selling or offering for sale of Finished VP Product, but not
             promoting or Detailing of VP Product, and shall include the receipt
             and storage of VP Product of the Aventis Launch Batches.

     1.38    "Effective Date" means September 9, 2001.

     1.39    "Exchange Act" means the Securities Exchange Act of 1934, as
             amended, or any successor federal statute and the rules and
             regulations of the SEC promulgated thereunder, all as the same
             shall be in effect from time to time.

     1.40    "FDA" means the United States Food and Drug Administration and any
             successor thereto.

     1.41    "FD&C Act" means the Federal Food, Drug, and Cosmetic Act, as
             amended, and all applicable regulations thereunder.

     1.42    "Field" means the use of a prescription pharmaceutical product to
             prevent or treat picornavirus infections in humans.

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     1.43    "Finance Subcommittee" or "FSC" means the committee described in
             Section 3.6.

     1.44    "Finished VP Product" means VP Product in finished packaged form
             (Sample or trade product), labeled and ready for sale or sampling
             and distribution in the Territory, and is used for the sake of
             clarity in provisions regarding or related to the Distribution or
             supply of VP Product for final sale.

     1.45    "First Indication" means the treatment of VRI in patients eighteen
             (18) years of age or older, i.e., adults.
                                         ----
     1.46    "FTE" means a full time equivalent person performing any activities
             under this Agreement, based on one thousand eight hundred eighty
             (1880) hours each year.

     1.47    "IND" means an investigational new drug application as defined in
             the FD&C Act.

     1.48    "Indication Development Budget Milestone" means for each Additional
             Indication, and for each Other Indication for which Aventis has
             elected to fund development activities pursuant to Section
             4.5.1(c)(ii), the amount proposed by the Development Subcommittee,
             approved by the JSC and included in the Development Plan and Budget
             representing the total expected costs of developing a VP Product
             for such Additional Indication or Other Indication.

     1.49    "Initial Supply Period" means the period starting from the
             Effective Date and ending twelve (12) months after the Launch Date.

     1.50    "Intellectual Work Product" means any and all data, regulatory
             filings, writings, research and test results, processes,
             formulations, reports, findings, conclusions, improvements,
             inventions, discoveries, methods of making or using VP Compounds or
             VP Product, work papers, notebook records, and any other
             information arising directly or indirectly from activities under
             this Agreement whether made or discovered by Aventis or any of its
             Affiliates, ViroPharma or any of its Affiliates, or any Third Party
             individually, or by any of the Parties and/or their Affiliates
             and/or such Third Parties jointly, except that know-how developed
             solely by ViroPharma to support prospective PCT applications
             filings or national or regional applications filed in relation
             thereto, which in any case claim priority to any U.S. provisional
             application filed before the Effective Date will be deemed
             ViroPharma Know-How.

     1.51    "IWP Patents" means any and all Patents claiming Intellectual Work
             Product.

     1.52    "Joint Steering Committee" or "JSC" means the committee described
             in Section 3.3.

     1.53    "Lapse Quarter" for a Party means, on a VP Product-by-VP Product
             basis in the Territory, any Calendar Quarter (beginning with the
             first full Calendar Quarter following the occurrence of Sale Force
             Parity) in which: (a) the Party's

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             Percentage of Assigned Effort is less than ****** percent
             (******%), and (b) such Percentage of Assigned Effort is at least
             ****** (******) ****** lower than the other Party's Percentage of
             Assigned Effort.

     1.54    "Lapse Year" for a Party means, on a VP Product-by-VP Product basis
             in the Territory, any Calendar Year in which such Party has ******
             (******) or more Lapse Quarters.

     1.55    "Launch Date" means the date on which the first VP Product is first
             shipped in commercial quantities for commercial sale to Third
             Parties other than contractors of a Party in the Territory.

     1.56    "Laws" means all laws, statutes, rules, regulations and ordinances
             (including Good Clinical Practice, Good Laboratory Practice and
             Good Manufacturing Practice) in effect in any jurisdiction of the
             Territory.

     1.57    "Major Company" means an entity which, as of December 31 of the
             Calendar Year immediately preceding a Change of Control of
             ViroPharma, had cash or cash equivalents (as reflected on its
             balance sheet), that combined with those of ViroPharma, are
             together in excess of five hundred million dollars
             (U.S.$500,000,000); provided, however, if an entity is not legally
             obligated to cover any indemnifiable claim Aventis may have related
             to the Termination Challenge as a result of such entity's corporate
             relationship with ViroPharma, then such entity shall not be a
             "Major Company" unless it provides adequate assurance, which is
             reasonably satisfactory to Aventis, that it will provide financial
             support to cover any indemnifiable claim Aventis may have related
             to the Termination Challenge.

     1.58    "Marketing Subcommittee" or "MSC" means the committee described in
             Section 3.4.

     1.59    "NDA" means a new drug application as defined in the FD&C Act, and
             includes a supplemental new drug application. 1.60 "Net Profits
             (Losses)" for a VP Product means Net Sales of such VP Product less
             Commercialization Expenses.

     1.61    "Net Sales" of a VP Product means the gross invoiced sales of such
             VP Product by a Party or its Affiliates to Third Parties other than
             contractors of a Party in the Territory after deducting:

             1.61.1  trade, cash and/or quantity discounts not already reflected
                     in the amount invoiced;

             1.61.2  excise, sales and other consumption taxes and custom duties
                     to the extent included in the invoice price;

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                                                                         Page 13
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             1.61.3  freight, insurance and other transportation charges to the
                     extent included in the invoice price;

             1.61.4  amounts repaid or credited by reason of rejections,
                     defects, recalls or returns (including in each case the
                     costs to destroy VP Product) or because of chargebacks,
                     refunds or billing errors, in each case to the extent
                     consistent with the Aventis Trade Policy;

             1.61.5  retroactive price reductions, and

             1.61.6  compulsory payments and rebates directly related to the
                     sale of VP Products, accrued, paid or deducted pursuant to
                     agreements (including, but not limited to, managed care
                     agreements) or governmental regulations.

             If a VP Product is sold as part of a Combination Product, the Net
             Sales of the VP Product, for the purposes of this Agreement, shall
             be equal to the Net Sales of the Combination Product multiplied by
             the amount AX/(AX + BY), where A is the weighted average net sales,
             defined as gross invoiced sales of the VP Product by a Party or its
             Affiliates to Third Parties other than contractors of a Party after
             deducting the amounts described in Sections 1.61.1-6, divided by
             the number of milligrams of VP Compound in such VP Product, B is
             the weighted average net sales, defined as gross invoiced sales of
             the other product to Third Parties other than contractors of a
             Party after deducting the amounts described in Sections 1.61.1-6,
             divided by the number of milligrams of therapeutically or
             prophylactically active ingredient(s) that is/are not a VP Compound
             in such product(s), X is the number of milligrams of VP Compound
             included in the Combination Product, and Y is the number of
             milligrams of the other therapeutically or prophylactically active
             ingredient(s) that is/are not a VP Compound in the Combination
             Product. For the sake of illustration and clarity only, a sample
             calculation is provided in Exhibit 1.61. If either variable A or B
             cannot be determined, the Net Sales of the VP Product as part of
             the Combination Product for purposes of this Agreement shall be
             agreed by the JSC based on the relative value contributed by each
             component, and such agreement shall not be unreasonably withheld.

     1.62    "Non-Serious Adverse Drug Experience" means any Adverse Drug
             Experience that is not a Serious Adverse Drug Experience.

     1.63    "Other Indication" means any indication in the Field other than the
             First Indication, the Second Indication or any Additional
             Indication, provided, however, that the indication of general
             prophylaxis of VRI shall be considered an Other Indication only if
             the JSC has approved such indication as an Other Indication
             pursuant to Section 4.4.2(e).

     1.64    "Patent" means any and all (a) patents, (b) pending patent
             applications, including, without limitation, all provisional
             applications, substitutions, continuations, continuations-in-part,
             divisions, renewals, and all patents granted

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                                                                         Page 14
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             thereon, and (c) all patents-of-addition, reissues, reexaminations
             and extensions or restorations by existing or future extension or
             restoration mechanisms, including, without limitation,
             supplementary protection certificates or the equivalent thereof.

     1.65    "Percentage of Assigned Effort" for a Party means the average of
             the percentage for each month of a Calendar Quarter (each monthly
             percentage not to exceed 100%) of Details assigned to such Party as
             Assigned Sales Force Effort for such month that such Party actually
             delivers in each such month.

     1.66    "Person" means any individual, partnership, joint venture,
             corporation, limited liability company, trust, unincorporated
             organization, government or department or agency of a government or
             other entity.

     1.67    "Phase 3a Study" means any study of a VP Product relating to an
             indication formulation, dose, course of therapy and patient
             population for which an NDA has been filed, conducted after the
             filing of such NDA, but which study is required to be performed by
             the Regulatory Authority before Regulatory Approval can be granted
             for such indication formulation, dose, course of therapy and
             patient population.

     1.68    "Phase 3b Study" means any study of a VP Product relating to an
             indication, formulation, dose, course of therapy and patient
             population for which an NDA has been filed, conducted after the
             filing of such NDA, which study is not required to be performed by
             the Regulatory Authority before Regulatory Approval can be granted
             for such indication formulation, dose, course of therapy and
             patient population, and which such study does not retroactively
             become a Phase 3a Study.

     1.69    "Phase 4 Study" means any study of a VP Product relating to an
             indication, formulation, dose, course of therapy and patient
             population for such VP Product, conducted after having received
             Regulatory Approval for such indication, formulation, dose, course
             of therapy and patient population.

     1.70    "Pleconaril" means the Compound pleconaril, 3-[3,5-dimethyl-4-[3-
             (3-methyl-5-isoxazolyl)propoxy]phenyl]-5-(trifluoromethyl)-1,2,4-
             oxadiazole, with CAS No. 153168-05-9, also known as VP 63843 and
             also named 5-{3-[2,6-dimethyl-4-(5-trifluoromethyl-1,2,4-ozadiazol-
             3-yl)phenoxy]propyl}-3-methylisoxazole in U.S. Patent No.
             5,464,848.

     1.71    "Primary Detail" means a Detail in which at least sixty percent
             (60%) of the total time of a Call is spent on a presentation of a
             VP Product or Aventis Product.

     1.72    "Primary Detail Equivalent" or "PDE" means either one Primary
             Detail or two Secondary Details.

     1.73    "Product Supplier" means a manufacturer or processor of VP Compound
             or VP Product for promotion and sale in the Territory, which
             manufacturer or processor is approved by the JSC, on the
             recommendation of the SCSC, and, to the extent necessary under the
             SaSy Agreement, SaSy.

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                                                                         Page 15
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     1.74    "Promotional Material" has the meaning set forth in Section 5.11.1.

     1.75    "Regulatory Approval" means the technical, medical and scientific
             licenses, registrations, authorizations and approvals (including,
             without limitation, approvals of NDAs, supplements and amendments,
             pre- and post-approvals, pricing approvals, and labeling approvals)
             of any national, supra-national, regional, state or local
             regulatory agency, department, bureau, commission, council or other
             governmental entity, necessary for the commercial manufacture,
             Distribution, marketing, promotion, offer for sale, use, import,
             export and sale of VP Product in a regulatory jurisdiction of the
             Territory.

     1.76    "Regulatory Authority" means any court, tribunal, arbitrator,
             agency, commission, official or other instrumentality of any
             federal, state, county, city or other political subdivision,
             domestic or foreign, including, without limitation, any authority
             over the development, manufacture, marketing or commercialization
             of VP Product.

     1.77    "Sales Force Parity" means the earlier of:

             1.77.1  the first day of the first Calendar Quarter in which the
                     number of PDEs allocated to ViroPharma for VP Products is
                     at least 95% of the number of PDEs assigned to Aventis for
                     VP Products, or

             1.77.2  if the Aventis representatives on the JSC have not voted in
                     favor of the request of ViroPharma to increase the number
                     of PDEs allocated to ViroPharma in a Calendar Quarter for
                     VP Products to a number that is at least 95% of the number
                     of PDEs assigned to Aventis for VP Products, then the date
                     of the Regulatory Approval in the United States of an NDA
                     for VP Product for the Second Indication.

     1.78    "Sample" means VP Product or Aventis Product, as applicable, to be
              determined by the MSC, that is not intended to be sold and is
              intended to promote the sale of such VP Product or Aventis
              Product. "Sample" shall mean a sample of VP Product, except in
              Article 9, where it shall mean a sample of Aventis Product, or
              unless otherwise specified.

     1.79    "SaSy" means Sanofi-Synthelabo, a corporation organized and
              existing under the laws of France.

     1.80    "SaSy Agreement" means that certain Amended and Restated Agreement
             dated February 27, 2001, between ViroPharma and SaSy, as amended
             from time to time hereinafter, but only as approved by Aventis.

     1.81    "SaSy Patents" means all of the U.S. Patents owned by SaSy and
             Controlled by ViroPharma, which Patents are listed in Exhibit 1.81.

     1.82    "SaSy Royalties" means any royalties required to be paid by
             ViroPharma to SaSy under the SaSy Agreement without regard to any
             deductions to such royalties

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                                                                         Page 16
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                     resulting from the payment by ViroPharma of any royalties
                     or other amounts to Third Parties as provided in the SaSy
                     Agreement, e.g., in connection with licensing certain
                     rights in order to practice SaSy Patents.

             1.83    "SEC" means the United States Securities and Exchange
                     Commission and any successor thereto.

             1.84    "Second Indication" means the treatment of VRI in patients
                     under eighteen (18) years old.

             1.85    "Second Indication Subset" means the treatment of VRI in
                     children between the ages of six (6) and twelve (12) years
                     old with a suspension formulation.

             1.86    "Secondary Detail" means a Detail in which at least thirty-
                     five percent (35%) of the total time of a Call is spent on
                     the presentation of VP Product or Aventis Product.

             1.87    "Serious Adverse Drug Experience" means any Adverse Drug
                     Experience that is fatal or life-threatening, is
                     permanently disabling, requires in-patient hospitalization,
                     or is a congenital anomaly, cancer or overdose, or any
                     other event which would constitute a "serious adverse drug
                     experience" within either of the definitions set forth at
                     21 C.F.R. (S) 314.80 and 21 C.F.R. (S) 312.32.

             1.88    "Shelf Life" means the period of time approved by FDA for
                     use in labeling for expiration dating of a VP Product.

             1.89    "Standstill Agreement" means that certain letter agreement
                     dated as of April 17, 2001 between Aventis and ViroPharma.

             1.90    "Supply Chain Subcommittee" or "SCSC" means the committee
                     described in Section 3.7.

             1.91    "Territory" means the United States.

             1.92    "Third Part(y/ies)" means any Person other than Aventis,
                     ViroPharma or their respective Affiliates.

             1.93    "Total Voting Power" means at any time the total combined
                     voting power in the general election of directors or
                     individuals with similar responsibilities of all the Voting
                     Securities then outstanding.

             1.94    "Trademarks" means those trademarks identified in, and the
                     trademark registrations issuing from, the applications
                     listed in Exhibit 1.94.

             1.95    "Uncurable ViroPharma Breach" means the breach, other than
                     a Curable ViroPharma Breach, by ViroPharma of:

                     1.95.1  Sections 2.6, or 2.7; or

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                                                                         Page 17
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                     1.95.2  any representation, warranty or covenant by or of
                             ViroPharma that has a material adverse effect on
                             the ability of Aventis to continue to develop,
                             promote, Detail and/or Distribute VP Products
                             consistent with the Development Plan and Budget or
                             the Commercialization Plan and Budget,

                     in each case, to the extent that ViroPharma has not
                     disputed the existence of a breach in good faith.

             1.96    "United States" or "U.S." means the United States of
                     America and its territories, commonwealths and possessions.

             1.97    "Valid Claim" means a claim of any unexpired United States
                     or foreign patent, that has not been donated to the public,
                     disclaimed, nor held invalid or unenforceable by a court or
                     government agency of competent jurisdiction in an
                     unappealed or unappealable decision.

             1.98    "ViroPharma Know-How" means all know-how, processes,
                     materials, information, data and analyses including any
                     copyright and trade secret related thereto to the extent
                     necessary or useful to develop, or to the extent necessary
                     to use, sell, or offer for sale VP Compounds or VP Products
                     in the Field, and that are owned or Controlled by
                     ViroPharma on the Effective Date or during the term of this
                     Agreement.

             1.99    "ViroPharma Logo" means the ViroPharma name logo set forth
                     on Exhibit 1.99, and all copyright and trademarks relating
                     thereto.

             1.100   "ViroPharma Patents" means any and all U.S. Patents owned
                     or Controlled by ViroPharma on the Effective Date covering
                     any VP Compound or VP Product other than SaSy Patents and
                     IWP Patents, which ViroPharma Patents are listed in Exhibit
                     1.100, and any other Patents owned or Controlled by
                     ViroPharma covering ViroPharma Know-How other than SaSy
                     Patents and IWP Patents.

             1.101   "ViroPharma Technology" means the ViroPharma Patents, SaSy
                     Patents, ViroPharma Know-How, the Trademarks and the
                     ViroPharma Logo.

             1.102   "Voting Securities" means at any time shares of any class
                     of capital stock of a Person which are then entitled to
                     vote generally in the election of directors.

             1.103   "VP 68881" means the Compound 5-(difluoromethyl)-3-[4-
                     [3-(5-ethyl-1,3,4-thiadiazol-2-yl)propoxy]-3,5-
                     dimethylphenyl]-1,2,4-oxadiazole, with CAS No. 172495-02-2,
                     and also named 2-ethyl-5-[3-[4-(5-difluoromethyl-1,2,4-
                     oxadiazol-3-yl)-2,6-dimethylphenoxy]propyl]-1,3,4-
                     thiadiazole in U.S. Patent No. 5,453,433.

             1.104   "VP Compound" means:

                     1.104.1  Pleconaril; and

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                                                                         Page 18
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                     1.104.2  VP 68881.

             1.105   "VP Product(s)" means any finished pharmaceutical
                     formulation, including bulk material, and Finished VP
                     Product, where applicable, for use in the Field that
                     contains a VP Compound as an active ingredient, and
                     includes any VP Product Exclusivity Unit.

             1.106   "VP Product Exclusivity Period" means for any VP Product
                     Exclusivity Unit sold in the Territory:

                     1.106.1   the period during which the Distribution and/or
                               promotion of the applicable VP Product
                               Exclusivity Unit in the Territory by any Person,
                               in the absence of a license granted by
                               ViroPharma, or in the case of IWP Patents,
                               ViroPharma and Aventis, to such Person, would
                               directly infringe one or more ViroPharma Patents,
                               SaSy Patents or IWP Patents, and

                     1.106.2   the period during which a Regulatory Authority
                               may not review or approve an application for
                               Regulatory Approval from a Third Party which
                               application relies on or refers to data included
                               in the NDA for such VP Product Exclusivity Unit,
                               which period immediately follows the expiration
                               of the period described in Section 1.106.1
                               without interruption.

             1.107   "VP Product Exclusivity Unit" means for any single
                     formulation of a VP Product, each combination of
                     indication, dose, dosing regimen, and, if applicable,
                     patient subpopulation, for which such formulation of VP
                     Product has received Regulatory Approval.

             1.108   "VP Product Target Prescribers" means a list of prescribing
                     physicians, developed by both Parties in conjunction with a
                     Third Party pharmaceutical marketing consultant acceptable
                     to both Parties, to whom the Detailing of VP Product will
                     optimize the value of such VP Product in the marketplace,
                     without regard to the effect of aligning a sales force to
                     such VP Product or the alignment of such sales force to
                     other products in either Party's portfolio, and which list
                     is based on an analysis of, among other things, physician
                     behavior, forecasted sales of VP Product, actual sales of
                     VP Product, if available, or of any other relevant product,
                     including, but not limited to, relevant products in either
                     Party's portfolio, and historical prescription data.

             1.109   "VRI" means viral respiratory infection.

             1.110   Additional Definitions. Each of the following definitions
                     is set forth in the Section of the Agreement indicated
                     below:

                     Definition                                  Section
                     ----------                                  -------
                     Audited Party..............................  8.11.2
                     Auditing Party.............................  8.11.2
                     Aventis....................................  Preamble
                     Aventis Indemnitees........................  15.1

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          Aventis Product........................................  9.2.1
          Commercialization Account..............................  5.8.2
          CSO....................................................  5.5.3(a)
          Development Account....................................  4.5.2
          Disclosing Party.......................................  1.24
          Force Majeure..........................................  17.4
          Form of Award..........................................  16.3.5
          Guidelines.............................................  5.16
          Indemnified Party......................................  15.3.1
          Indemnifying Party.....................................  15.3.1
          Initial Commercialization Plan and Budget..............  5.3.1
          Initial Development Plan and Budget....................  4.4.1
          ******.................................................  8.1.2
          Litigation Conditions..................................  15.3.2
          Notified Party.........................................  17.4
          OTC Lock-Out Period....................................  2.7.4
          Party(ies).............................................  Preamble
          PDMA...................................................  5.13.1
          Receiving Party........................................  1.24
          SaSy Breach Dispute....................................  10.6.1(b)
          SaSy Dispute...........................................  10.6.3(b)
          Section 10.6.2 Breach Challenge........................  10.6.2(c)
          Termination Challenge..................................  12.4.2
          Third Party Claim......................................  15.3.1
          ViroPharma.............................................  Preamble
          ViroPharma Indemnitees.................................  15.2

2.  LICENSES.

    2.1  License to Aventis. Subject to the terms of this Agreement, ViroPharma
         hereby grants to Aventis the royalty-free, non-sublicensable, except as
         set forth in Sections 2.3, 2.4, 2.5, 2.7.2, and 2.7.3 right and license
         in the Territory and in the Field to use the ViroPharma Technology only
         to the extent necessary to:

         2.1.1  develop and use VP Compounds;

         2.1.2  promote and Detail VP Products;

         2.1.3  import Finished VP Product from a Product Supplier of Finished
                VP Product into the Territory;

         2.1.4  export to Canada, but only if ViroPharma or any of its
                Affiliates has entered into a written copromotion agreement for
                VP Product for Canada with a Canadian Affiliate of Aventis, VP
                Compounds or VP Products; and

         2.1.5  Distribute VP Products;

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                                                                         Page 20
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                     in each case only to the extent provided in this Agreement,
                     which right and license shall be exclusive, except as to
                     ViroPharma and its Affiliates for Sections 2.1.1, 2.1.2,
                     2.1.3, and 2.1.4, and exclusive even as to ViroPharma and
                     its Affiliates for Section 2.1.5, except as otherwise
                     provided in this Agreement. Except as otherwise provided in
                     this Agreement, Aventis shall have no right or license
                     hereunder to make, have made, or repackage in the Territory
                     any VP Product or VP Compound.

            2.2      License to ViroPharma. Subject to the terms of this
                     Agreement, and as permitted by any agreement between
                     Aventis and a Third Party in effect as of the Effective
                     Date, Aventis hereby grants to ViroPharma the royalty-free,
                     non-exclusive, and non-sublicensable, except as set forth
                     in Section 2.5, right and license in the Territory to use
                     the Aventis Technology, but only to the extent necessary to
                     develop, make, have made, use, Detail, import, or export VP
                     Compounds or VP Products pursuant to this Agreement.

             2.3     Aventis Sublicensing of Distribution to Aventis Affiliates
                     and Third Parties. ViroPharma hereby grants to Aventis the
                     right to sublicense Aventis' Distribution, importation into
                     the Territory from a Product Supplier of VP Product or
                     exportation to Canada, but only if ViroPharma or any of its
                     Affiliates has entered into a written copromotion agreement
                     for VP Product for Canada with a Canadian Affiliate of
                     Aventis, of VP Product in the Territory to one or more of
                     Aventis' Affiliates in the Territory or to Third Parties
                     that perform such activities for Aventis' top fifteen (15)
                     prescription pharmaceutical products in the Territory.

             2.4     Sublicensing of Detailing, Marketing and Promotion to
                     Affiliates and Third Parties. Either Party may sublicense
                     its Detailing, marketing or promotion of VP Products to an
                     Affiliate of such Party and to Third Parties, as provided
                     for herein. Notwithstanding the foregoing, the Party
                     selecting an Affiliate to perform tasks under this
                     Agreement shall be solely responsible for activities
                     performed by such Affiliate, and the selection and use of
                     an Affiliate shall not relieve such Party of its
                     obligations hereunder.

             2.5     Sublicensing/Subcontracting to Third Parties.

                     2.5.1  Either Party may select a Third Party to perform
                            certain tasks under this Agreement, including,
                            without limitation, any development, marketing,
                            sales, Detailing, or Distribution if and only to the
                            extent as provided for in this Agreement. The Party
                            entering into a contract with such Third Party for
                            the performance of such services, may, as part of
                            such contract, grant to such Third Party a
                            nonexclusive, nontransferable, non-sublicensable
                            license or sublicense, as applicable, under the
                            ViroPharma Technology and Aventis Technology, only
                            to the extent and only for so long as such license
                            or sublicense is necessary for such Third Party to
                            perform such tasks. Notwithstanding the foregoing,
                            the Party selecting a Third Party to perform tasks
                            under this Agreement shall be solely responsible for

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                                                                         Page 21
<PAGE>

                     activities performed by such Third Party, and the selection
                     and use of a Third Party shall not relieve such Party of
                     its obligations hereunder.

             2.5.2   As a condition to entering into such sublicense or
                     subcontract:

                     (a)   a Party shall exercise commercially reasonable
                           efforts to obtain a provision in such sublicense or
                           subcontract stating that such sublicense or
                           subcontract shall be freely assignable to the other
                           Party, and the first Party shall notify the other
                           Party if the first Party was unable to obtain such a
                           provision, and the Parties shall consult on how to
                           proceed, but in no case shall such inability to
                           obtain an assignability provision, notwithstanding
                           the exercise of commercially reasonable efforts,
                           prevent such first Party from entering into the
                           agreement; and

                     (b)   the sublicensor/subcontractor must undertake in
                           writing obligations of confidentiality and non-use
                           regarding the other Party's Confidential Information
                           which are at least as restrictive with regard to such
                           sublicensor/subcontractor as those undertaken by
                           Aventis or ViroPharma pursuant to Article 11 hereof.

     2.6     Exclusive Relationship. Notwithstanding the licenses granted under
             Sections 2.1 and 2.2 hereof, the Parties expressly understand and
             agree that during the term of this Agreement:

             2.6.1   Neither Party shall directly or indirectly make, have made,
                     develop, use, sell, or offer for sale in the Territory, or
                     import into the Territory any VP Compound or VP Product,
                     except in collaboration with the other Party as set forth
                     in this Agreement.

             2.6.2   Neither Party shall directly or indirectly make, have made,
                     develop, use, sell, or offer for sale (or sell or license
                     to an Affiliate or Third Party the right to make, have
                     made, develop, use, sell or offer for sale) in the
                     Territory, or import into the Territory a Compound or
                     product (other than a VP Compound or VP Product) in the
                     Field for any indication that is the First Indication or
                     the Second Indication ****** except in collaboration with
                     the other Party as set forth in this Agreement.

             2.6.3   Subject to Section 2.6.2, neither Party shall directly or
                     indirectly make, have made, develop, use, sell, or offer
                     for sale (or sell or license to an Affiliate or Third Party
                     the right to make, have made, develop, use, sell or offer
                     for sale) in the Territory, or import into the Territory a
                     Compound or product (other than a VP Compound or VP
                     Product) in the Field for any or all of the following
                     indications:

                     (a)  an indication for which the Parties are ******,

                     (b)  an indication for which the Parties ****** pursuant to
                          a ******,

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                                                                         Page 22
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                 (c)  an indication for which the Parties ****** pursuant to and
                      as set forth in a ******;

                 unless (i) either (a) for indications ******, such Party
                 proposes to the JSC and the other Party's representatives on
                 the JSC ****** within sixty (60) days of such proposal or (b)
                 the JSC has decided to ******, and (ii) ****** is at least
                 ****** by the Parties to ******, after ****** described in
                 ******.

          2.6.4  Aventis shall not directly or indirectly export out of the
                 Territory any VP Compound or VP Product, except in
                 collaboration with ViroPharma, and shall not directly or
                 indirectly develop, use, sell, offer for sale, have sold, make
                 and have made, import and export, any VP Product or VP Compound
                 outside the Territory, except under a license from SaSy as
                 contemplated by Section 2.8, and only to the extent of such
                 license.

          For the sake of clarity, nothing in this Section 2.6 shall prevent
          either Party from performing any preclinical research on any
          Compounds.

     2.7  OTC Rights.

          2.7.1  Exclusion. Except as set forth in Sections 2.7.2 and 2.7.3, it
                 is expressly understood that this Agreement grants Aventis no
                 rights to directly or indirectly make, have made, develop, use
                 sell or offer for sale in the Territory, or import into the
                 Territory, or export from one part to another part of the
                 Territory, or export out of the Territory, or share in any
                 revenue from the sale of any VP Compound or VP Product for use
                 or sale as other than a prescription pharmaceutical product,
                 and that ViroPharma retains all such rights.

          2.7.2  Forced OTC Switch. If a Regulatory Authority requires that any
                 VP Product Exclusivity Unit be sold in the Territory without
                 prescription labeling restrictions before the expiration of the
                 VP Product Exclusivity Period for such VP Product Exclusivity
                 Unit, (a "Forced OTC Switch") then the right and license to
                 such VP Product Exclusivity Unit granted to Aventis under
                 Section 2.1 shall include using, developing, Distributing,
                 promoting, Detailing, importing from a Product Supplier of VP
                 Product into the Territory, or exporting to Canada, but in the
                 case of exporting, only if ViroPharma or any of its Affiliates
                 has entered into a written copromotion agreement for VP Product
                 for Canada with a Canadian Affiliate of Aventis, such VP
                 Product Exclusivity Unit for the indication of such VP Product
                 Exclusivity Unit, without regard to prescription or over-the-
                 counter status. Upon a Forced OTC Switch, the JSC shall decide
                 whether or not to commercialize such VP Product Exclusivity
                 Unit in the OTC market, and whether or not to continue
                 commercializing any related VP Product Exclusivity Unit in the
                 prescription market. Neither Party shall be obligated to
                 commercialize such VP Product Exclusivity Unit

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                                                                         Page 23
<PAGE>

                 itself, to the extent such Party does not have OTC
                 commercialization abilities; and the JSC shall agree on any
                 Third Party that shall perform the commercialization activities
                 for such VP Product Exclusivity Unit on behalf of either or
                 both Parties. The JSC shall then amend the then-current
                 Commercialization Plan and Budget to reflect such decision, and
                 the Parties shall negotiate in good faith any required
                 amendments to this Agreement, provided that (a) the Net Profits
                 from the sales of such VP Product Exclusivity Unit shall
                 continue to be divided as set forth in Section 8.4, and (b) the
                 Development Expenses and Commercialization Expenses shall
                 continue to be divided as set forth in this Agreement. The
                 provision of this Section 2.7.2 shall apply to each VP Product
                 Exclusivity Unit that is subject to a Forced OTC Switch before
                 the expiration of such VP Product Exclusivity Unit's VP Product
                 Exclusivity Period. Notwithstanding any other provision of this
                 Agreement, ViroPharma shall not be entitled to exercise its
                 buy-out rights under Section 2.7.5 from and after the
                 occurrence of a Forced OTC Switch.

          2.7.3  Voluntary OTC Switch. If the JSC decides to sell any VP Product
                 Exclusivity Unit in the Territory without prescription labeling
                 restrictions (a "Voluntary OTC Switch"), then the right and
                 license to such VP Product Exclusivity Unit granted to Aventis
                 under Section 2.1 shall include using, developing,
                 Distributing, promoting, Detailing, importing from a Product
                 Supplier of VP Product into the Territory, or exporting to
                 Canada, but in the case of exporting, only if ViroPharma or any
                 of its Affiliates has entered into a written copromotion
                 agreement for VP Product for Canada with a Canadian Affiliate
                 of Aventis, such VP Product Exclusivity Unit for the indication
                 of such VP Product Exclusivity Unit, without regard to
                 prescription or over-the-counter status. Neither Party shall be
                 obligated to commercialize such VP Product Exclusivity Unit
                 itself, to the extent such Party does not have OTC
                 commercialization abilities; and the JSC shall agree on any
                 Third Party that shall perform the commercialization activities
                 for such VP Product Exclusivity Unit on behalf of either or
                 both Parties. The JSC shall then amend the then-current
                 Commercialization Plan and Budget to reflect such decision, and
                 the Parties shall negotiate in good faith any required
                 amendments to this Agreement, provided that (a) the Net Profits
                 from the sales of such VP Product Exclusivity Unit shall
                 continue to be divided as set forth in Section 8.4, and (b) the
                 Development Expenses and Commercialization Expenses shall
                 continue to be divided as set forth in this Agreement. This
                 Section 2.7.3 shall apply to each VP Product Exclusivity Unit
                 that is subject to a Voluntary OTC Switch before the expiration
                 of such VP Product Exclusivity Unit's VP Product Exclusivity
                 Period.

          2.7.4  Restriction. Except as set forth in Section 2.7.2, 2.7.3 or
                 2.7.5, ViroPharma shall not directly or indirectly sell or
                 offer for sale (or license to an Affiliate or Third Party the
                 right to sell or offer for sale) as an over-the-counter
                 pharmaceutical product in the Territory any VP Product

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                                                                         Page 24
<PAGE>

                 Exclusivity Unit, until the date ****** (******) ****** before
                 the expiration of the applicable VP Product Exclusivity Period
                 covering such VP Product Exclusivity Unit (the "OTC Lock-Out
                 Period"). Except as set forth in Section 2.7.2, or 2.7.3, for
                 each VP Product Exclusivity Unit, after the OTC Lock-Out
                 Period, ViroPharma shall not directly or indirectly sell or
                 offer for sale (or license to an Affiliate or Third Party the
                 right to sell or offer for sale) as an over-the-counter
                 pharmaceutical product in the Territory such VP Product
                 Exclusivity Unit unless such VP Product Exclusivity Unit ******
                 at any time during the ****** (******) ****** before the
                 expiration of the applicable VP Product Exclusivity Period.

          2.7.5  Rx Tail Buyout.

                 (a)  Right of First Negotiation. Subject to Section 2.7.5(c),
                      if ViroPharma intends to directly or indirectly sell or
                      offer for sale any VP Product Exclusivity Unit as an over-
                      the-counter pharmaceutical product in the Territory after
                      the expiration or termination of the OTC Lock-Out Period
                      in the U.S., but during the term of this Agreement, then
                      no sooner than ****** (******) ****** before the
                      expiration of the applicable VP Product Exclusivity Period
                      in the U.S. covering such VP Product Exclusivity Unit,
                      ViroPharma shall give Aventis written notice of such
                      intention, and for the sixty (60) day period following the
                      date of such notice, the Parties shall negotiate
                      exclusively with each other, commercial terms under which
                      Aventis and ViroPharma would commercialize such VP Product
                      Exclusivity Unit over-the-counter. Neither Party shall be
                      obligated to agree upon any such terms or to accept any
                      terms proposed by the other Party.

                 (b)  Rx Tail Buyout. If ViroPharma decides to sell any VP
                      Product as an over-the-counter pharmaceutical product in
                      the Territory, then, after the completion of the sixty
                      (60) day period set forth in Section 2.7.5(a), and no
                      earlier than ****** (******) ****** before the expiration
                      of the first to expire VP Product Exclusivity Period in
                      the U.S. covering any VP Product Exclusivity Unit that
                      ****** at any time during the ****** (******) ******
                      before the expiration of the applicable VP Product
                      Exclusivity Period in the Territory, ViroPharma shall
                      provide Aventis with written notice of such decision,
                      causing a valuation of the Aventis Interest, as of the
                      date ****** (******) ****** before the expiration of the
                      first to expire VP Product Exclusivity Period in the U.S.
                      or such later date specified by ViroPharma (either, the
                      "ViroPharma OTC Launch Date"), pursuant to the procedures
                      set forth in Sections 12.5.3-4. Such valuation of the
                      Aventis Interest shall be the "Rx Tail Buyout Price." On
                      the ViroPharma OTC Launch Date, ViroPharma shall pay
                      Aventis the Rx Tail Buyout Price in readily available U.S.

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                                                                         Page 25
<PAGE>

                      Dollars. Upon the payment to Aventis of the Rx Tail Buyout
                      Price, this Agreement shall terminate.

                 (c)  This Section 2.7.5 shall terminate and no longer be in
                      force or effect upon the earlier to occur of:

                      (i)   A Forced OTC Switch, or

                      (ii)  A Voluntary OTC Switch in which Aventis is
                            performing substantially all of the
                            commercialization activities for the VP Product
                            Exclusivity Unit(s) subject to the Voluntary OTC
                            Switch.

     2.8  Extra-Territorial Licensing. ViroPharma shall use its commercially
          reasonable efforts to assist Aventis, at Aventis' expense for
          ViroPharma's pre-approved and documented out-of-pocket costs, in
          acquiring from SaSy rights for Aventis to: (a) develop, use, sell,
          offer for sale, have sold, make and have made, import and export, any
          VP Product in Japan, and (b) market and/or promote any VP Product
          outside the Territory and Japan. Upon, and to the extent of, the
          acquisition from SaSy, by Aventis, of rights to make and have made VP
          Compounds or VP Products outside the Territory, then to the extent
          permitted by SaSy, by the SaSy Agreement and any agreement with a
          Product Supplier, and to the extent not unreasonably disruptive to
          ViroPharma, ViroPharma will use commercially reasonable efforts to
          transfer technology for manufacturing VP Compounds and VP Products
          from Product Suppliers or ViroPharma to Aventis. Aventis shall
          reimburse ViroPharma's pre-approved and documented out-of-pocket costs
          for such technology transfer.

     2.9  Section 365(n) of the Bankruptcy Code. All rights and licenses granted
          under or pursuant to any section of this Agreement are, and shall
          otherwise be deemed to be, for purposes of Section 365(n) of the
          Bankruptcy Code, licenses of rights to "intellectual property" as
          defined under Section 101(35A) of the Bankruptcy Code. The Parties
          shall retain and may fully exercise all of their respective rights and
          elections under the Bankruptcy Code. Upon the bankruptcy of any Party
          to which 365(n) applies, the non-bankrupt Party shall further be
          entitled to a complete duplicate of (or complete access to, as
          appropriate) any such intellectual property to which it is otherwise
          entitled under this Agreement, and such, if not already in its
          possession, shall be promptly delivered to the non-bankrupt Party,
          unless the bankrupt Party elects to continue, and continues, to
          perform all of its obligations under this Agreement.

3.   MANAGEMENT OF COLLABORATION.

     3.1  Compliance with Laws. The Parties shall perform all activities under
          this Agreement in compliance with all Laws and with any applicable
          professional standards.

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                                                                         Page 26
<PAGE>

     3.2  Cooperative Activities Generally. Subject to the other provisions of
          this Agreement, each Party shall use commercially reasonable efforts
          to perform each of its obligations under this Agreement including,
          without limitation, the intent of maximizing the financial return to
          the Parties hereunder, and acting in a manner that is otherwise in the
          best interests of the collaboration formed hereunder. Each Party shall
          perform its obligations under this Agreement in good faith and with
          fair dealing.

     3.3  Joint Steering Committee.

          3.3.1  The Parties shall establish a Joint Steering Committee which
                 shall have as its overall purpose the development,
                 implementation and management of commercial planning activities
                 and research and development programs with respect to VP
                 Compounds and VP Products, each consistent with the other. The
                 Joint Steering Committee shall have such subcommittees (in
                 addition to the Marketing Subcommittee, the Development
                 Subcommittee, the Finance Subcommittee and the Supply Chain
                 Subcommittee described below) as the Parties or the JSC may
                 mutually agree from time to time hereafter. The JSC shall
                 consist of a number of from two (2) to ten (10) representatives
                 from each Party drawn from among such Party's senior managers.
                 Within thirty (30) days after the Effective Date each Party
                 shall appoint two (2) members to the JSC. Either Party may
                 replace one or more of its members on the JSC by providing
                 notice to the other Party. The JSC shall, in addition to such
                 other responsibilities as are assigned to it herein, review the
                 activities of the Marketing Subcommittee, the Development
                 Subcommittee, the Finance Subcommittee, the Supply Chain
                 Subcommittee and any other subcommittees formed from time to
                 time, and seek to resolve any matter upon which any such
                 subcommittee is unable to make a decision, except as otherwise
                 provided herein. Among its other responsibilities, but without
                 limitation, the JSC solely shall be responsible for:

                 (a)  approving any proposed Commercialization Plan and Budget,
                      including the long term forecast made pursuant to Section
                      6.4.10, and Development Plan and Budget submitted to it by
                      the Marketing Subcommittee or the Development
                      Subcommittee,

                 (b)  approving any proposed material amendment to any
                      Commercialization Plan and Budget, including the long term
                      forecast made pursuant to Section 6.4.10, and Development
                      Plan and Budget submitted to it by the Marketing
                      Subcommittee or the Development Subcommittee,

                 (c)  managing the VP Product life cycle and intellectual
                      property protection, and identifying the extent to which
                      any Intellectual Work Product likely to result from
                      development activities being

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                                                                         Page 27
<PAGE>

                      considered by the JSC would be subject to ownership or
                      Control by a Third Party, consistent with Section 10.1.2;

                 (d)  approving any and all prices for VP Product throughout the
                      Territory proposed by the MSC including any and all ranges
                      of discount amounts within which the MSC shall have
                      discretion to operate, and any material changes to the
                      Aventis Trade Policy affecting the treatment of VP Product
                      returns and refunds,

                 (e)  approving the list of VP Product Target Prescribers, the
                      allocation of Details to be performed by each Party among
                      VP Product Target Prescribers, and any material changes to
                      such allocation,

                 (f)  approving the Launch Date proposed by the MSC, and the
                      date of launch of any subsequent VP Product Exclusivity
                      Unit throughout the Territory,

                 (g)  reviewing and approving any plans and budgets prepared
                      jointly by the MSC and the DSC for any Phase 3b Studies,
                      Phase 4 Studies, or health outcome studies for VP Product,

                 (h)  approving any study protocol and any material amendment
                      thereto for any phase 3 study (including Phase 3a Studies
                      and Phase 3b Studies) for the Second Indication;

                 (i)  for any Other Indication and any Additional Indication,
                      approving any clinical study protocol, and material
                      amendments thereto for phase 2 or phase 3 study activities
                      performed under this Agreement,

                 (j)  approving the recommendation of the SCSC for new Product
                      Suppliers, subject to approval by SaSy,

                 (k)  for any Other Indication and any Additional Indication,
                      approving any INDs and NDAs to be submitted to Regulatory
                      Authority and any material labeling changes to any VP
                      Product.

     3.4  Marketing Subcommittee.

          3.4.1  Formation and Meetings. The JSC shall establish a Marketing
                 Subcommittee which shall have as its overall purpose the
                 development and implementation of commercialization activities
                 for VP Products in the Territory. The Marketing Subcommittee
                 shall consist of a number of from two (2) to four (4), as
                 determined by the JSC, representatives from each Party drawn
                 from among such Party's senior sales and marketing managers.
                 Each Party shall assign members to the Marketing Subcommittee
                 at the request of the JSC, and each Party may replace one or
                 more of such members by providing notice to the other Party.

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                                                                         Page 28
<PAGE>

          3.4.2  Duties.  The Marketing Subcommittee shall:

                 (a)  prepare, and review on a quarterly basis, the
                      Commercialization Plan and Budget, subject to the final
                      approval of the Commercialization Plan and Budget by the
                      JSC; and

                 (b)  subject to, and within the constraints of, any approved
                      Commercialization Plan and Budget:

                      (i)    oversee the implementation of the Commercialization
                             Plan and Budget, and ensure that each Party
                             executes its responsibilities described in such
                             Commercialization Plan and Budget;

                      (ii)   develop and discuss strategies for the Detailing
                             and marketing of VP Products in the Territory,
                             including allocation of responsibility for
                             marketing activities, and support through
                             professional education;

                      (iii)  in collaboration with the DSC, deciding whether to
                             perform, and then preparing any plans and budgets
                             for any Phase 3b Studies, Phase 4 Studies, and
                             health outcome studies for VP Product;

                      (iv)   propose to the JSC the Launch Date, and the date of
                             launch for any subsequent VP Product;

                      (v)    propose to the JSC the price for VP Product
                             throughout the Territory and any and all ranges of
                             discount amounts within which the MSC shall have
                             discretion to operate, and any material changes to
                             the Aventis Trade Policy affecting the treatment of
                             VP Product returns and refunds, and establish the
                             conditions of distribution and sale of VP Product;

                      (vi)   propose to the JSC the list of VP Product Target
                             Prescribers and the allocation of Details to be
                             performed by each Party among VP Product Target
                             Prescribers, or material changes to such
                             allocations previously approved by the JSC;

                      (vii)  develop and agree upon strategies and procedures
                             for, and give approval to, the use of Third Parties
                             to perform commercialization activities other than
                             Distribution, manufacturing, and with respect to
                             the use of CSOs, subject to Section 5.5.3;

                      (viii) review progress of commercialization activities
                             against the current Commercialization Plan and
                             Budget;

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                                                                         Page 29
<PAGE>

                      (ix)    review the rate of spending on commercialization
                              activities against the budget for such activities
                              in the Commercialization Plan and Budget;

                      (x)     propose the long term forecasts of VP Product
                              needs pursuant to Section 6.4.10 for approval by
                              the JSC;

                      (xi)    prepare short term forecasts of VP Product needs
                              pursuant to Section 6.4.11;

                      (xii)   compare actual VP Product sales against sales
                              forecasts and targets set out in the
                              Commercialization Plan and Budget;

                      (xiii)  consider, and propose to the JSC, potential
                              amendments to the Commercialization Plan and
                              Budget;

                      (xiv)   establish working groups to implement the
                              Commercialization Plan and Budget;

                      (xv)    present the results of commercialization efforts
                              to the JSC;

                      (xvi)   undertake all other activities necessary to manage
                              the marketing and sale of VP Product in the
                              Territory;

                      (xvii)  any other duties that are delegated to the
                              Marketing Subcommittee by the JSC; and

                 (c)  review and comment on the semi-annual report on the
                      Parties' commercialization activities under this Agreement
                      prepared by ViroPharma, for submission to SaSy.

     3.5  Development Subcommittee.

          3.5.1  Formation and Meetings. The JSC shall establish a Development
                 Subcommittee which shall have as its overall purpose the
                 development, implementation and management of development
                 activities for VP Compounds and VP Products in the Territory.
                 The Development Subcommittee shall consist of a number of from
                 two (2) to four (4), as determined by the JSC, representatives
                 from each Party drawn from among such Party's senior
                 development managers. Each Party shall assign members to the
                 Development Subcommittee at the request of the JSC, and each
                 Party may replace one or more of such members by providing
                 notice to the other Party.

          3.5.2  Duties.  The Development Subcommittee shall:

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                                                                         Page 30
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                 (a)  prepare, and review on a quarterly basis, the Development
                      Plan and Budget, subject to the final approval of the
                      Development Plan and Budget by the JSC;

                 (b)  subject to, and within the constraints of any approved
                      Development Plan and Budget, and to the extent applicable
                      to Sections 3.5.2(b)(ii-iii), any approved
                      Commercialization Plan and Budget:

                      (i)    oversee the implementation of the Development Plan
                             and Budget, and ensure that each Party executes its
                             responsibilities described in such Development Plan
                             and Budget;

                      (ii)   in collaboration with the MSC, decide whether to
                             perform, and then prepare any plans and budgets for
                             any Phase 3b Studies, Phase 4 Studies, and health
                             outcome studies for VP Product

                      (iii)  implement, and review the progress of studies of VP
                             Product, including Phase 3b Studies, Phase 4
                             Studies, and health outcome studies;

                      (iv)   review the rate of spending on development
                             activities against the budget for such activities
                             in the Development Plan and Budget;

                      (v)    review the filing of any INDs and submission of
                             protocols to such INDs;

                      (vi)   review the filing of any NDAs, to the extent
                             provided for in Section 7.1.1;

                      (vii)  present the results of development efforts to the
                             JSC;

                      (viii) undertake all other activities necessary to manage
                             the development of VP Product in the Territory; and

                      (ix)   consider, and propose to the JSC, potential
                             amendments to the Development Plan and Budget; and

                      (x)    any other duties that are delegated to the
                             Development Subcommittee by the JSC;

                 (c)  review and comment on the semi-annual report on the
                      Parties' development activities under this Agreement
                      prepared by ViroPharma, for submission to SaSy.

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                                                                         Page 31
<PAGE>

     3.6  Finance Subcommittee.

          3.6.1  Formation and Meetings. The JSC shall establish a Finance
                 Subcommittee which shall have as its overall purpose the
                 management of finance and accounting matters for activities of
                 the Parties under this Agreement. The Finance Subcommittee
                 shall consist of two (2) representatives from each Party with
                 financial and accounting expertise assigned to such
                 subcommittee by each Party. Each Party may replace one or more
                 of such members by providing notice to the other Party.

          3.6.2  Duties.  The Finance Subcommittee shall:

                 (a)  assure the prompt sharing between the Parties of accurate
                      financial information regarding activities under this
                      Agreement;

                 (b)  provide advice to the JSC and other subcommittees of the
                      JSC regarding the allocation of resources by the Parties;

                 (c)  establish a method for recording the Development Costs and
                      Commercialization Expenses attributable to the development
                      and commercialization of VP Product for each indication;

                 (d)  agree on the application as appropriate of United States
                      Generally Accepted Accounting Principles to the accounting
                      of the Parties with respect to activities under the
                      Agreement;

                 (e)  to the extent applicable, agree on the inclusion in
                      Commercialization Expenses of the cost for the Product
                      Supplier of Finished VP Product to bill for the full Cost
                      of Goods for Finished VP Product, including costs of
                      manufacturing activities not performed by such final
                      Product Supplier;

                 (f)  provide input and review all budgets proposed by any other
                      subcommittee under this Agreement;

                 (g)  review the rate of spending by the Parties compared to the
                      applicable budget for such activities; and

                 (h)  establish performance goals and requirements and perform
                      reviews to determine if the Parties meet the applicable
                      performance goals and requirements.

     3.7  Supply Chain Subcommittee.

          3.7.1  Formation and Meetings. The JSC shall establish a Supply Chain
                 Subcommittee which shall have as its overall purpose the
                 management of

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                                                                         Page 32
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                 the supply of VP Product to the Parties under this Agreement.
                 The Supply Chain Subcommittee shall consist of a number of from
                 two (2) to four (4) representatives from each Party with
                 manufacturing and supply expertise assigned to such
                 subcommittee by each Party. Each Party may replace one or more
                 of such members by providing notice to the other Party.

          3.7.2  Duties. Subject to the terms of this Agreement, except as
                 otherwise provided in Section 6.2, the Supply Chain
                 Subcommittee shall:

                 (a)  oversee and manage the ordering, manufacture and supply of
                      Finished VP Product to the Parties in accordance with the
                      forecast supplied by the MSC,

                 (b)  prepare a supply plan coordinating the entire supply chain
                      to support the Development Plan and Budget and the
                      Commercialization Plan and Budget,

                 (c)  propose new Product Suppliers to the JSC for approval;

                 (d)  oversee all manufacturing of VP Compound, all micronizing
                      of VP Compound, and all manufacturing and packaging of VP
                      Product,

                 (e)  make all necessary adjustments to the manufacturing
                      schedules to ensure meeting the requirements of the
                      Commercialization Plan and Budget with respect to supply
                      of Finished VP Product,

                 (f)  schedule the shipment of Finished VP Product to Aventis,

                 (g)  manage all inventory levels of VP Compound and VP Product,

                 (h)  manage any and all rejections of VP Compound or VP Product
                      along the entire supply chain,

                 (i)  identify and take actions to prevent potential
                      interruptions of VP Product supply,

                 (j)  perform capacity analysis,

                 (k)  plan and implement process improvements, cost reduction
                      initiatives, logistics initiatives, and environmental
                      health and safety initiatives, and

                 (l)  oversee and implement all Quality Assurance, Quality
                      Control and GMP activities.

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                                                                         Page 33
<PAGE>

3.8  Meetings.

     3.8.1  Chairperson and Secretary. The chairperson of the JSC and of each
            subcommittee shall be selected from among the members of the JSC or
            the subcommittee, as applicable, and shall serve a one-year term.
            ViroPharma will select the first chairperson of the JSC, the
            Development Subcommittee, and the Supply Chain Subcommittee, and
            Aventis will select the first chairperson of the Marketing
            Subcommittee and Finance Subcommittee, and the selection of
            chairpersons shall alternate annually between the Parties
            thereafter. The chairperson will be responsible for scheduling
            meetings of the committee or subcommittee, preparing agendas for
            meetings, and sending all committee or subcommittee members notices
            of all regular meetings and agendas for such meetings at least five
            (5) business days before such meetings. The chairperson shall
            appoint a secretary for the committee or subcommittee who shall not
            be a member thereof, and who will record the minutes of each
            meeting, circulate copies of meeting minutes to the Parties and each
            committee or subcommittee member promptly following the meeting for
            review, comment and approval and finalize approved meeting minutes
            before the next meeting.

     3.8.2  Attendance, Voting and Authority. Meetings of the JSC or one of its
            subcommittees shall be effective only if at least one representative
            of each Party designated to represent such Party on the JSC or such
            subcommittee is in attendance or participating in the meeting.
            Members of the JSC and its subcommittees shall have the right to
            participate in meetings by telephone. Representatives of either
            Party who are not members of the JSC or any subcommittee may attend
            meetings of such committee or subcommittee with the consent of the
            committee members of the other Party. Third Parties may attend or
            present at meetings of the JSC or any subcommittee only with the
            prior consent of the entire committee or subcommittee. Each Party
            shall have one (1) vote at meetings of the JSC or any of its
            subcommittees.

     3.8.3  Frequency of Meetings; Timing of Meetings. The JSC and each
            subcommittee shall meet with such frequency and at such times and at
            such places as the members of the JSC or such subcommittee shall
            determine, but not less often than twice per Calendar Year for the
            JSC and DSC, and at least quarterly for the MSC, FSC and SCSC.

     3.8.4  Expenses. Each Party shall be responsible for lodging and travel
            expenses incurred by its employees and its members of the JSC and
            subcommittees attending or otherwise participating in such meetings.
            Any common expenses for such meetings shall be shared equally
            between the Parties.

3.9  Budgets. The initial process to begin preparing each budget required under
     this Agreement shall begin sufficiently early so that a draft budget can be
     submitted to the JSC for review no later than August 31 of the year
     preceding the Calendar

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                                                                         Page 34
<PAGE>

      Year to which such budget applies. Each Party will reasonably cooperate
      with each other to finalize the budgets in a time period consistent with
      the Parties' internal budgeting process; provided, however, that each
      budget shall be finalized and approved by the JSC no later than December
      15 of the year in which such budget is submitted to the JSC. Each budget
      required under this Agreement shall be subject to the review of the
      Finance Subcommittee.

3.10  Decision Making and Dispute Resolution.

      3.10.1  Subcommittees.

              (a)  MSC. All decisions of the MSC shall be made consistent with,
                   and within the financial constraints of, the then-applicable,
                   approved Commercialization Plan and Budget. All decisions of
                   the MSC shall be made by unanimous decision of the Parties,
                   except that if the MSC is unable to reach unanimous decision
                   on any issue, the Aventis representatives on the MSC shall
                   have the deciding vote, except:

                   (i)  for such matters as are reserved for the approval of the
                        JSC, and

                   (ii) as otherwise provided for in Section 3.10.6.

                   Notwithstanding the foregoing, except for Sections
                   3.10.1(a)(i-ii), day-to-day operational activities required
                   to be performed in the ordinary course may be implemented by
                   Aventis without the prior consent of the MSC so long as
                   consistent with and within the financial and operational
                   constraints of the then-applicable approved Commercialization
                   Plan and Budget.

              (b)  DSC. All decisions of the DSC shall be made consistent with,
                   and within the financial constraints of, the then-applicable,
                   approved Development Plan and Budget. All decisions of the
                   DSC shall be made by unanimous decision of the Parties,
                   except that if the DSC is unable to reach unanimous decision
                   on any issue, the ViroPharma representatives on the DSC shall
                   have the deciding vote, except

                   (i)   for such matters as are reserved for the approval of
                         the JSC,

                   (ii)  as to the outsourcing to Third Parties of development
                         activities for amounts greater than ****** (******) per
                         contract, and

                   (iii) as otherwise provided in Section 3.10.6.

                   Notwithstanding the foregoing, except for Sections
                   3.10.1(b)(i-ii),

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                                                                         Page 35
<PAGE>

                   day-to-day operational activities required to be performed in
                   the ordinary course may be implemented by ViroPharma without
                   the prior consent of the DSC so long as consistent with and
                   within the financial and operational constraints of the then-
                   applicable approved Development Plan and Budget.

              (c)  JSC, Finance Subcommittee, and Supply Chain Subcommittee. All
                   decisions of the JSC, the Finance Subcommittee and the Supply
                   Chain Subcommittee shall be made by unanimous decision of the
                   Parties.

     3.10.2   JSC. If for any reason a subcommittee of the JSC is unable to
              reach a decision that requires unanimity in accordance with
              Section 3.10.1 within a reasonable period of time, but in no event
              to exceed thirty (30) days, the matter shall be referred to the
              JSC for resolution. All decisions of the JSC shall be made by
              unanimous decision of the Parties.

     3.10.3   Heads of Commercial Operations. If for any reason the Joint
              Steering Committee cannot reach a unanimous decision on any matter
              within a reasonable period of time, but in no event to exceed
              thirty (30) days, or if the JSC cannot reach a decision on any
              matter referred to it pursuant to Section 3.10.2 within thirty
              (30) days of such matter being referred to it, then the matter
              shall be referred to ViroPharma's head of Commercial Operations
              and Aventis' head of U.S. Commercial Operations for good faith
              resolution, except as otherwise provided in Section 3.10.6.

     3.10.4   Final Internal Dispute Resolution. If for any reason ViroPharma's
              head of Commercial Operations and Aventis' head of U.S. Commercial
              Operations cannot resolve a matter referred to them by the JSC
              within thirty (30) days of such matter being referred to them,
              then the matter shall be referred to ViroPharma's CEO and the Head
              of Aventis North America for good faith resolution.

     3.10.5   Arbitration. If for any reason ViroPharma's CEO and the Head of
              Aventis North America cannot resolve a matter referred to them by
              ViroPharma's head of Commercial Operations and Aventis' head of
              U.S. Commercial Operations within thirty (30) days of such matter
              being referred to them, then the matter will be referred for
              binding arbitration as set forth in Article 16, except as
              otherwise provided in Section 3.10.6.

     3.10.6   Exceptions.

              (a)  If the DSC or the JSC is unable to decide any issue with
                   regard to the activities to be performed and the amounts to
                   be spent under the Initial Development Plan and Budget and
                   the amounts to be spent under Section 4.1.2(c), then such
                   items shall be implemented as written in this Agreement and
                   such issues shall not be subject to

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                                                                         Page 36
<PAGE>

                   the dispute resolution provisions of Sections 3.10.3, 3.10.4
                   or 3.10.5.

              (b)  If the MSC or the JSC is unable to decide any issue with
                   regard to the amounts to be spent pursuant to Section 5.3.1,
                   or the number of PDEs to be performed pursuant to Section
                   5.4.1, then such items shall be implemented as written in
                   this Agreement and such issues shall not be subject to the
                   dispute resolution provisions of Sections 3.10.3, 3.10.4 or
                   3.10.5, except that issues regarding the allocation of PDEs
                   between Aventis and ViroPharma and/or the number of PDEs to
                   be performed in the event that Section 5.4.1 does not apply
                   because ******, shall be subject to the dispute resolution
                                   -----
                   provisions of Sections 3.10.3, 3.10.4 and 3.10.5.

              (c)  If ViroPharma concludes that any Promotional Material does
                   not comply with the FD&C Act, then the Parties shall not use
                   such Promotional Material, Aventis' representatives on the
                   MSC shall not have the deciding vote on such matter, and such
                   matter shall not be subject to the dispute resolution
                   provisions of Sections 3.10.2, 3.10.3, 3.10.4 or 3.10.5.

              (d)  If ViroPharma's CEO and the head of Aventis North America are
                   unable to reach agreement on:

                   (i)   the price to be charged for any VP Product in the
                         Territory, any range of discounts to be applied to such
                         price, or any material changes to the Aventis Trade
                         Policy affecting the treatment of VP Product returns or
                         refunds,

                   (ii)  the selection after the Effective Date of any Product
                         Supplier other than those listed in Exhibit 6.4.7(a),

                   (iii) whether or not to initiate, continue or discontinue the
                         development of any VP Product for the First Indication,
                         the Second Indication, or any Other Indication or the
                         approval of any items in the Development Plan and
                         Budget (or any amendments to such plan and budget)
                         relating to such initiation or continued development,
                         except to the extent addressed in Section 3.10.6(a),

                   (iv)  whether or not to implement a Voluntary OTC Switch,

                   (v)   whether to initiate any study that would cause the
                         total Development Expenses spent for the Additional
                         Indications to exceed ****** dollars ($******) for a
                         single Additional Indication or ****** dollars
                         ($******) for both Additional Indications or the
                         approval of any items in the Commercialization Plan and
                         Budget or the Development

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                                                                         Page 37
<PAGE>

                         Plan and Budget (or any amendments to such plan and
                         budgets) relating to such initiation,

                   then neither Party shall have the sole right to make the
                   final decision and such issue shall not be subject to the
                   dispute resolution provisions of Sections 3.10.5.

4.   DEVELOPMENT.

     4.1  Development Program.

          4.1.1  Generally. ViroPharma will perform all development activities
                 assigned to it in the Development Plan and Budget, either
                 itself, or through an Affiliate or, subject to Sections 2.5 and
                 3.10.1(b)(ii), a Third Party contractor, including, without
                 limitation, clinical or preclinical studies in order to obtain
                 initial Regulatory Approval of any VP Product and to support
                 future labeling changes or new indications of VP Products in
                 accordance with the Development Plan and Budget, and Phase 3b
                 Studies, Phase 4 Studies, and health outcome studies in order
                 to further the commercialization of VP Products in accordance
                 with the Commercialization Plan and Budget. The Development
                 Subcommittee will manage and oversee the implementation of
                 development activities under the Development Plan and Budget
                 and will select those indications and labeling enhancements to
                 be pursued under the Development Plan and Budget.

          4.1.2  First, Second and Additional Indications. Notwithstanding
                 anything to the contrary in any Development Plan and Budget,
                 the Parties agree to develop the First Indication, the Second
                 Indication and Additional Indications as follows:

                 (a)  First Indication. The Parties shall perform the studies
                      and other activities described in the Initial Development
                      Plan and Budget for VP Product for the First Indication.

                 (b)  Second Indication. The Parties shall perform the
                      development activities through the end of the phase 2
                      studies described in the Initial Development Plan and
                      Budget for VP Product for the Second Indication. If such
                      phase 2 studies ****** in the United States ******, then
                      the JSC shall review the results from such studies ******.
                      If the JSC ******in the United States ******.

                 (c)  Additional Indications. After the Effective Date, the JSC
                      shall approve an Indication Development Budget Milestone
                      of ****** dollars ($******) for the first Additional
                      Indication to receive Regulatory Approval in the U.S. and
                      ******dollars ($******) for the second Additional
                      Indication to receive Regulatory Approval in the U.S. and
                      a Development Plan and Budget reflecting such

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                                                                         Page 38
<PAGE>

                      Indication Development Budget Milestones. If an arbitrator
                      does not require the Parties to perform studies for the
                      Additional Indications, or if Aventis refuses to initiate
                      any study that would cause the total Development Expenses
                      spent for the Additional Indications to exceed ******
                      dollars ($******) for a single Additional Indication or
                      ****** dollars ($******) for both Additional Indications,
                      then ViroPharma shall ******, and such ****** subject
                      ****** under ******.

4.2  Development Efforts. To the extent development activities have been
     delegated to a Party under the Development Plan and Budget, such Party
     shall use commercially reasonable efforts to achieve the objectives and
     milestones set forth in the Development Plan and Budget within the
     timeframe set forth therein and to develop the VP Compounds into VP
     Products. In furtherance of the foregoing, each Party shall deploy
     sufficient personnel and other resources to achieve such milestones and
     objectives set forth in the Development Plan and Budget.

4.3  Development Regulatory Activities. ViroPharma shall be solely responsible
     for seeking and obtaining Regulatory Approval from Regulatory Authorities
     to perform activities under the Development Plan and Budget, including,
     without limitation, filing any INDs and submitting protocols to such INDs
     as approved by the JSC as necessary. ViroPharma shall use commercially
     reasonable efforts to extend the VP Product Exclusivity Period for each VP
     Product. Within twenty (20) days after submission to FDA, ViroPharma shall
     provide Aventis with copies of all material final submissions to such INDs
     for studies performed under the Development Plan and Budget. Consistent
     with Laws, up to three (3) Aventis representatives shall be permitted to
     attend all meetings and conferences with any Regulatory Authority in the
     Territory concerning VP Compounds or VP Products.

4.4  Development Plan and Budgets.

     4.4.1  Initial Development Plan and Budget. The Development Plan and Budget
            for all development activities for the First Indication and Second
            Indication is attached to this Agreement as Exhibit 4.4.1 (the
            "Initial Development Plan and Budget").

     4.4.2  Subsequent Development Plan and Budgets. As early as necessary in
            each year beginning with the first full Calendar Year after the
            Effective Date, the Development Subcommittee shall commence the
            process of preparing the Development Plan and Budget for the
            following Calendar Year so that it can submit such proposed
            Development Plan and Budget to the JSC no later than August 31 of
            such year for review. In no event shall later Development Plans and
            Budgets conflict with the Initial Development Plan and Budget
            without the unanimous consent of the JSC. Each Development Plan and
            Budget shall contain at minimum:

            (a)  a comprehensive VP Product development strategy;

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                                                                         Page 39
<PAGE>

            (b)  a list and timeline for the performance of studies in support
                 of the development activities;

            (c)  an overall budget for development activities during the
                 relevant Calendar Year;

            (d)  a phase 3b and phase 4 clinical development plan established in
                 collaboration with the MSC, and in compliance with the
                 Commercialization Plan and Budget;

            (e)  a statement setting out for which, if any, of the Other
                 Indications the Parties intend to initiate or continue
                 development of VP Product during the relevant Calendar Year,
                 defining with specificity each such Other Indication; and

            (f)  a complete and comprehensive budget for the development of:

                 (i)   each Additional Indication, and

                 (ii)  each Other Indication, and

                 (iii) for each Other Indication for which ******, the
                       Indication Development Budget Milestone for such Other
                       Indication.

4.5  Development Funding.

     4.5.1  Division of Expenses Generally. The Parties shall share the
            Development Expenses as follows:

            (a)  First Indication and Second Indication. Aventis shall be
                 responsible for fifty percent (50%) and ViroPharma shall be
                 responsible for fifty percent (50%) of the Development Expenses
                 incurred in connection with the development of any VP Product
                 for the First Indication or for the Second Indication.

            (b)  Additional Indications. ViroPharma shall initially bear ******
                 the Development Expenses incurred in connection with the
                 development of any VP Product for any Additional Indication.
                 Upon Regulatory Approval of such VP Product for an Additional
                 Indication, Aventis shall pay ViroPharma the Indication
                 Development Budget Milestone for such Additional Indication as
                 set forth in Section 8.3. In addition, within thirty (30) days
                 of the payment of any Indication Development Budget Milestone:

                 (i)   ViroPharma shall pay Aventis ****** (******) of the
                       amount by which the Indication Development Budget
                       Milestone exceeds the actual Development Expenses for
                       development activities provided for in the Development

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                                                                         Page 40
<PAGE>

                       Plan and Budget or otherwise approved in advance by the
                       JSC for the development of the VP Product for the
                       Additional Indication for which the Indication
                       Development Budget Milestone was paid; and

                 (ii)  Aventis shall pay ViroPharma ****** (******) of the
                       amount by which the actual Development Expenses for
                       development activities provided for in the Development
                       Plan and Budget or otherwise approved in advance by the
                       JSC for the development of the VP Product for the
                       Additional Indication for which the Indication
                       Development Budget Milestone was paid exceed the
                       Indication Development Budget Milestone. If Regulatory
                       Approval for such VP Product for such Additional
                       Indication is obtained after ******, the amount to be
                       paid by Aventis under this Section 4.5.1(b)(ii) shall be
                       reduced to the following percentages of the total set
                       forth in the previous sentence (the "Base Amount"):

                 Calendar Year During Which
                 Regulatory Approval of VP        Percentage of the Base Amount
                 Product for Additional           to be Paid by Aventis to
                 Indication Is Obtained           ViroPharma
                 ---------------------------      ------------------------
                       ******                              ******%
                       ******                              ******%
                       ******                              ******%
                       ******                              ******%.

            (c)  Other Indications. Before the JSC's approval of a Development
                 Plan and Budget that includes development activities of a VP
                 Product for any Other Indication, as such Other Indication has
                 been identified and defined by the Development Committee in
                 such Development Plan and Budget as set forth in Section
                 4.4.2(e), Aventis shall choose one of the two following funding
                 methods, which choice may not later be changed, and shall
                 notify the Finance Subcommittee of its choice, and if Aventis
                 has not notified the FSC of such choice by the date on which
                 the JSC approves the applicable Development Plan and Budget,
                 then Aventis shall be deemed to have chosen the funding method
                 described in Section 4.5.1(c)(ii):

                 (i)   Aventis shall be responsible for ****** percent (******%)
                       and ViroPharma shall be responsible for ****** percent
                       (******%) of the Development Expenses incurred in

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                                                                         Page 41
<PAGE>

                       connection with the development of such VP Product for
                       such Other indication; or

                 (ii)  ViroPharma shall ****** bear ****** the Development
                       Expenses for such VP Product for such Other Indication,
                       and upon Regulatory Approval of such VP Product for such
                       Other Indication, Aventis shall pay ViroPharma the
                       Indication Development Budget Milestone for such Other
                       Indication as set forth in Section 8.3. In addition,
                       within thirty (30) days of the payment of any Indication
                       Development Budget Milestone:

                       a.  ViroPharma shall pay Aventis ****** of the amount by
                           which the Indication Development Budget Milestone
                           exceeds the actual Development Expenses for
                           development activities provided for in the
                           Development Plan and Budget or otherwise approved in
                           advance by the JSC for the development of such VP
                           Product for such Other Indication for which the
                           Indication Development Budget Milestone was paid; and

                       b.  Aventis shall pay ViroPharma ****** of the amount by
                           which the actual Development Expenses for development
                           activities provided for in the Development Plan and
                           Budget or otherwise approved in advance by the JSC
                           for the development of such VP Product for such Other
                           Indication for which the Indication Development
                           Budget Milestone was paid exceed the Indication
                           Development Budget Milestone.

          4.5.2  Payment of Expenses; Development Account. Subject to
                 reconciliation as provided in Section 8.5, each Party shall be
                 responsible and pay for all Development Expenses incurred in
                 performing its obligations in connection with any development
                 activities under the Development Plan and Budget. Each Party
                 shall charge all such expenses so incurred to a separate
                 account created by it on its books and records solely for the
                 purpose of tracking Development Expenses, identifying all
                 Development Expenses by the VP Product and indication being
                 developed (the "Development Account").

          4.5.3  Cost Overruns. Each month ViroPharma shall review Development
                 Expenses actually charged or to be charged to its Development
                 Account against the applicable Development Plan and Budget. In
                 the event that ViroPharma determines that any such actual or
                 anticipated expenses relating to the approved activities in the
                 Development Plan and Budget

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                                                                         Page 42
<PAGE>

                 will exceed the applicable Development Plan and Budget, it
                 shall promptly notify the DSC which shall meet as soon as
                 reasonably possible. The DSC shall review the reasonableness of
                 such expenses in light of the overall Development Plan and
                 Budget and shall propose an appropriate amendment, if
                 necessary, to the Development Plan and Budget to the JSC for
                 approval.

5.   COMMERCIALIZATION.

     5.1  General. Under the terms and conditions set forth herein and pursuant
          to the licenses granted in Article 2, ViroPharma and Aventis shall
          collaborate in the promotion, Detailing and Distribution of VP
          Products in the Territory, including, without limitation, performing
          epidemiological modeling, pharmacoeconomic, actual use and any other
          Phase 3b Studies or Phase 4 Studies, subject to the Commercialization
          Plan and Budget and the oversight of the Marketing Subcommittee.

     5.2  Commercialization Efforts. To the extent commercialization activities
          have been delegated to a Party under the Commercialization Plan and
          Budget, such Party shall use commercially reasonable efforts to
          achieve the objectives and milestones set forth in the
          Commercialization Plan and Budget within the timeframe set forth
          therein and to commercialize the VP Products. In furtherance of the
          foregoing, each Party shall deploy sufficient personnel and other
          resources to achieve such milestones and objectives set forth in the
          Commercialization Plan and Budget.

     5.3  Commercialization Plans and Budgets.

          5.3.1  Initial Commercialization Plan and Budget. The Marketing
                 Subcommittee shall propose to the JSC a Commercialization Plan
                 and Budget for all marketing, sales and educational activities
                 up to the Launch Date within three (3) months after the
                 Effective Date (the "Initial Commercialization Plan and
                 Budget"). The Initial Commercialization Plan and Budget adopted
                 by the JSC shall provide for minimum funding by the Parties of
                 promotional activities, not including PDEs, as follows:

                 (a)  at least ****** U.S. dollars (U.S. $******) from the
                      Effective Date through the end of Calendar Year ******,

                 (b)  at least ****** U.S. dollars (U.S. $******) from ******
                      until ******,

                 (c)  at least ****** U.S. dollars (U.S. $******) from ******
                      until the date ****** (******) ****** after ******.

                 If the Initial Commercialization Plan and Budget is not
                 finalized in accordance with this Section 5.3.1, then the
                 amounts described herein shall constitute such budget.
                 Notwithstanding the foregoing, if VP

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                                                                         Page 43
<PAGE>

                 Product to be launched on the Launch Date ******, then neither
                 party shall be required to spend the amounts set forth in this
                 Section 5.3.1, and instead, each Party shall be required to
                 spend the amounts determined by the JSC.

          5.3.2  Subsequent Commercialization Plans and Budgets. As early as
                 necessary in each Calendar Year, the Marketing Subcommittee
                 shall begin the process of preparing a revised four-year
                 Commercialization Plan and Budget which shall include an
                 additional Calendar Year, so that it can submit such proposed
                 Commercialization Plan and Budget to the JSC no later than
                 August 31 of such year for review. Each Commercialization Plan
                 and Budget shall contain at minimum:

                 (a)  a comprehensive market development, marketing, product
                      positioning, sales, supply, and distribution strategy for
                      VP Products in the Territory;

                 (b)  the most recent long term forecasts of VP Product needs
                      prepared pursuant to Section 6.4.10;

                 (c)  a budget for commercialization activities during the
                      relevant Calendar Years, including, without limitation,
                      allocations for advertising, promotional and educational
                      meetings and activities, Detail Cost of VP Product, field
                      force micro-marketing, alignment and direction,
                      distribution of Samples, and Phase 3b and Phase 4 Studies;

                 (d)  the number and positioning of Details to be performed by
                      each Party in each month of each Calendar Quarter of such
                      Calendar Year in the Territory consistent with Section
                      5.4, and the number of Details on VP Product Target
                      Prescribers called upon;

                 (e)  VP Product pricing and contracting strategies;

                 (f)  a phase 3b and phase 4 clinical development plan
                      established in collaboration with the DSC;

                 (g)  the managed care strategy and deployment plan; and

                 (h)  the VP Product positioning and key message strategy.

     5.4  Assigned Sales Force Effort. The MSC shall determine the number of
          Details to be performed, the type of Details to be performed, and
          shall allocate Details on VP Product Target Prescribers between
          Aventis and ViroPharma for each Calendar Quarter in the Territory
          consistent with the allocation set out in each approved
          Commercialization Plan and Budget, and with the following standards:

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                                                                         Page 44
<PAGE>
          5.4.1   Launch Details. Unless otherwise agreed to by the JSC, and
                  provided that quantities of VP Product and VP Product Samples
                  are available, the Parties shall perform, ******, if (i)
                  either (x) no sooner than three (3) months before the expected
                  Regulatory Approval of an NDA for VP Product for the Second
                  Indication, ViroPharma has requested that the JSC increase the
                  number of PDEs allocated to ViroPharma in a Calendar Quarter
                  for VP Products to a number that is at least 95% of the number
                  of PDEs assigned to Aventis for VP Products, or (y) the JSC
                  has approved an allocation of PDEs to ViroPharma that is at
                  least 95% of the number of PDEs assigned to Aventis for VP
                  Products, and (ii) ViroPharma has sufficient sales
                  representatives to perform such PDEs or (b) ******, if the
                  conditions in Section 5.4.1(a)(i-ii) are not met , in each
                  case ******. Notwithstanding the foregoing, if a VP Product
                  ******, then ****** required to ****** set forth in this
                  Section 5.4.1 ****** each Party shall be required to ******.
                  At least ****** percent (******%) of the Primary Details of VP
                  Product required to be performed by either Party pursuant to
                  this Section 5.4.1 shall be made to VP Product Target
                  Prescribers.

          5.4.2   Targeting. Each Party shall perform Details of VP Product
                  allocated to it by the Commercialization Plan and Budget only
                  to VP Product Target Prescribers that does not require a
                  geographical realignment of the sales representatives of such
                  Party, unless otherwise determined by the JSC.

          5.4.3   Managed Care and Other National Account Allocation. Aventis
                  shall, using commercially reasonable efforts, perform all
                  visits to managed care accounts, trade accounts, government
                  accounts, and other national accounts.

          5.4.4   Suspension for Low Pipeline Supply. If and for so long as, at
                  any time after the Launch Date, there is less than one week's
                  supply of VP Product in the pipeline at the wholesale level as
                  reported by IMS Pipeline, then the obligation to perform
                  Details, as set forth herein, shall be suspended, unless
                  otherwise determined by the MSC.

     5.5  Detailing Effort.

          5.5.1   Efforts. Each Party shall deploy sufficient sales
                  representatives to promote and Detail each VP Product in the
                  Territory effectively in accordance with the terms of this
                  Agreement and the applicable Commercialization Plan and
                  Budget. In conducting such promotion and Detailing, both
                  Aventis and ViroPharma shall use at least commercially
                  reasonable efforts consistent with the efforts it applies to
                  prescription drug products of comparable peak sales potential
                  in the U.S., and if the ****** of such VP Product ******,
                  consistent with the efforts it applies to prescription drug
                  products, with comparable ******, of comparable peak sales
                  potential in the U.S.

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                                                                         Page 45
<PAGE>
     5.5.2  Beginning of Detailing. Each Party shall give prompt written notice
            to the other of the date on which its sales representatives begin
            Detailing any VP Product in the Territory.

     5.5.3  Sales Representatives.

            (a)  All Details performed by each Party under this Agreement shall
                 be performed by sales representatives who are employees of such
                 Party or of such Party's Affiliates in the Territory, except
                 that either Party may use the services of a contract sales
                 organization ("CSO") to assist such Party in performing Details
                 as follows:

                 (i)   If ViroPharma is promoting and Detailing an Aventis
                       Product pursuant to Article 9, ViroPharma may use a CSO
                       to perform PDEs in excess of ****** per year,

                 (ii)  Aventis may use a CSO to perform PDEs in excess of ******
                       per year,

                 (iii) Any sales representative of such CSO performing Details
                       for either Party shall have at least six (6) months
                       experience performing Details in the pharmaceutical
                       industry and shall have received training comparable to
                       the training provided by a Party to its own sales
                       representatives.

                 Any Detail performed by an employee of such CSO consistent with
                 a Party's allocation under Section 5.4, this Section 5.5.3(a),
                 and the Commercialization Plan and Budget shall be considered a
                 Detail performed by such Party.

            (b)  Unless ****** before the Launch Date, then beginning on the
                 later of ****** or ******, at least ****** percent (******%) of
                 the Details performed by ViroPharma under this Agreement shall
                 be performed by sales representatives who have worked for
                 ViroPharma or its Affiliates in the Territory for at least six
                 (6) months. In the case of Aventis, beginning on the Launch
                 Date, at least ****** percent (******%) of the Details
                 performed by Aventis shall be performed by sales
                 representatives of Aventis who have worked for Aventis or its
                 Affiliates in the Territory in a primary care sales force for
                 at least six (6) months.

     5.6    Detailing Performance Incentive. If either Party performs less than
            ******% of the PDEs assigned to it in any Calendar Quarter, such
            Party shall pay to the other Party an amount equal to ****** (the
            "Missed Detail Payment"). If a Party performs ******% or more, but
            less than 100%, of the PDEs assigned to it, in lieu of paying the
            Missed Detail Payment, such Party may make up such shortfall by
            performing the same type and number of Details in another Calendar
            Quarter selected by the non-defaulting Party. If such Party fails to
            make up 100% of the

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                                                                         Page 46
<PAGE>
            shortfall of PDEs in such other Calendar Quarter, then such Party
            shall pay to the other Party the Missed Detail Payment for each PDE
            that it failed to perform in such Calendar Quarter. Payments by a
            Party under this Section 5.6 shall be made directly to the other
            Party within sixty (60) days of the end of the applicable Calendar
            Quarter. Any Missed Detail Payment shall not be treated as a
            Commercialization Expense.

     5.7    Detailing Reports and Record Retention.

            5.7.1  Detail Metrics. The number of Details actually performed by
                   either Party shall be determined according to Detail
                   reporting mechanisms and methodology that are approved and
                   applied consistently by the Marketing Subcommittee.
                   Notwithstanding the foregoing, a Party shall be credited with
                   performing a Detail only if such Detail is performed in
                   accordance with the Commercialization Plan and Budget, the
                   Party's allocation under Section 5.4, and this Agreement
                   generally.

            5.7.2  Reports.

                   (a)  First Twelve Weeks. For the first twelve (12) weeks
                        after the Launch Date, each Party shall provide to the
                        other both a preliminary and final report of the number
                        of Details carried out by its representatives during
                        each week in such period. Preliminary reports shall be
                        delivered to the other Party no later than three (3)
                        weeks after the end of the applicable week and final
                        reports shall be delivered no later than six (6) weeks
                        after the end of the applicable week.

                   (b)  First Two Years. After the end of the reporting period
                        of Section 5.7.2(a) and through the end of the first
                        full Calendar Year after the Launch Date, each Party
                        shall provide the other both a preliminary and final
                        report of the number of Details carried out by its
                        representatives during each month. Preliminary reports
                        shall be delivered to the other Party no later than
                        three (3) weeks after the end of the applicable month
                        and final reports shall be delivered no later than six
                        (6) weeks after the end of the applicable month.

                   (c)  Thereafter. Beginning after the first full Calendar Year
                        after the Launch Date, for the Term of the Agreement,
                        each Party shall provide the other both a preliminary
                        and final report of the number of Details carried out by
                        its representatives during each Calendar Quarter.
                        Preliminary reports shall be delivered to the other
                        Party within three (3) weeks of the end of the
                        applicable Calendar Quarter and final reports shall be
                        delivered six weeks after the end of the applicable
                        Calendar Quarter.

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          5.7.3  Detail Records. Each Party shall keep accurate and complete
                 records of each Detail performed by such Party, its Affiliates,
                 or permitted contract sales organizations under this Agreement
                 and shall make such records available for inspection, review
                 and audit by an independent certified public accountant
                 appointed by the other Party and reasonably acceptable to such
                 Party for the purpose of verifying the number of Details made
                 by such Party.

     5.8  Commercialization Expenses; Funding.

          5.8.1  Commercialization Expenses. Subject to the terms of this
                 Agreement, Aventis shall pay fifty-five percent (55%) and
                 ViroPharma shall pay forty-five percent (45%) of all
                 Commercialization Expenses incurred by either Party in the
                 Territory.

          5.8.2  Payment of Expenses; Commercialization Accounts. Subject to
                 reconciliation as provided in Section 8.5, each Party shall be
                 responsible and pay for the Commercialization Expenses incurred
                 for any VP Product in the Territory. Each Party shall charge
                 all such expenses so incurred by it or its Affiliates to a
                 separate account created by such Party on its books and records
                 solely for the purpose of tracking Commercialization Expenses
                 incurred in connection with any VP Product in the Territory (a
                 "Commercialization Account"). Each Party shall submit to the
                 other Party a written summary of all Commercialization Expenses
                 incurred by it for any VP Product in the Territory as described
                 in Section 8.5.1.

          5.8.3  Reimbursement of Commercialization Expenses.

                 (a)  Reimbursement Principles. Within the timeframe described
                      in Sections 8.5.3 and 8.5.4, Commercialization Expenses:

                      (i)   properly charged by such Party to its
                            Commercialization Account,

                      (ii)  reported to the other Party in accordance with this
                            Section 8.5.1, and

                      (iii) on a VP Product-by-VP Product basis, attributable to
                            the sale of such VP Product in the Territory,

                      shall be reimbursed in accordance with the principles of
                      Sections 8.5.3 and 8.5.4.

     5.9  Sales Force Compensation.

          5.9.1  Compensation Plan. Each Party shall pay incentive compensation
                 to its sales representatives having primary responsibility for
                 Detailing VP Products with respect to sales of VP Product in
                 the Territory. Each Party

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                   shall implement an incentive product weighting for its sales
                   representatives for VP Product in its sales force incentive
                   plan ("SICP") generally consistent with incentive weighting
                   given to its sales representatives for its other primary care
                   products which are assigned the same product Detail position
                   as the VP Product is assigned in the Commercialization Plan
                   and Budget.

     5.10  Customer Orders and Distribution.

           5.10.1  Generally. Except as contemplated or set forth elsewhere in
                   this Agreement, including, without limitation, Article 6,
                   Aventis shall have the sole right to:

                   (a)  receive, accept and fill orders for Finished VP Product

                   (b)  control invoicing, order processing and collection of
                        accounts receivable for Finished VP Product sales,

                   (c)  record Finished VP Product inventory in its books of
                        account,

                   (d)  record Finished VP Product sales in its books of
                        account,

                   (e)  perform all activities required for the Distribution of
                        any Finished VP Product, and

                   (f)  establish and modify the commercial terms and conditions
                        with respect to the Distribution of Finished VP Product,
                        other than the price for Finished VP Product including
                        any and all ranges of discount amounts within which the
                        MSC shall have discretion to operate, and any material
                        changes to the Aventis Trade Policy affecting the
                        treatment of Finished VP Product returns and refunds.

          5.10.2   Misdirected Customer Orders. If, for any reason, ViroPharma
                   receives customer orders for Finished VP Product, ViroPharma
                   shall forward such orders to Aventis, or if directed by
                   Aventis to Aventis' wholesalers, as soon as practicable.

          5.10.3   VP Product Returns. If any quantities of Finished VP Product
                   are returned to ViroPharma, ViroPharma shall immediately
                   notify Aventis and ship them to the facility designated by
                   Aventis. All returns of Samples used by ViroPharma's field
                   force shall first be returned to ViroPharma who shall ship
                   them to Aventis.

     5.11 Promotional Materials.

          5.11.1   Development and Production. The Marketing Subcommittee shall
                   create and develop advertising, promotional, educational and
                   communication materials for marketing, advertising and
                   promotion of VP

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                   Product for Distribution to independent Third Parties
                   (including medical professionals) and to ViroPharma's and
                   Aventis' respective sales forces in accordance with the terms
                   of the Commercialization Plan and Budget (the "Promotional
                   Materials"). A committee consisting of representatives of
                   each of the legal, regulatory and medical departments of
                   ViroPharma, and of Aventis, if requested by Aventis, (the
                   "LRMC") shall review such Promotional Materials to confirm
                   their compliance with Laws. Promotional Materials shall be
                   approved by the LRMC only by the unanimous consent of the
                   representative on the LRMC. The MSC shall only release for
                   marketing, advertising and promotion of VP Product such
                   Promotional Materials approved by the LRMC. The Marketing
                   Subcommittee shall ensure that adequate Promotional Materials
                   are provided to each Party's respective sales forces.

           5.11.2  Limitation. Each Party shall use only Promotional Materials,
                   labels and labeling relating to VP Product created and
                   approved in accordance with Section 5.11.1. Neither Party may
                   independently create, distribute or use Promotional
                   Materials, labels or labeling relating to VP Product without
                   the prior written consent of either the Marketing
                   Subcommittee or the other Party.

           5.11.3  Recalls and Corrections of Promotional Materials. The Parties
                   shall share equally all costs resulting from the failure of
                   Promotional Materials approved by the LRMC to comply with
                   Laws. Any such costs, including, without limitation, costs
                   for recalls of, or other corrections of, any Promotional
                   Materials shall be treated as a Commercialization Expense.

     5.12  Promotional Claims. Each Party shall limit the claims of safety and
           efficacy that such Party or its sales force makes for VP Product to
           those that are consistent with the approved labeling for such VP
           Product in the Territory. Neither Party may add, delete or modify
           claims of efficacy or safety in its promotion of VP Product in the
           Territory nor make any changes in Promotional Materials created and
           approved in accordance with Section 5.11.1.

     5.13  Samples of VP Product.

           5.13.1  General. Samples shall be allocated between the Parties based
                   on the number and type of Details each Party is required to
                   undertake pursuant to the Commercialization Plan and Budget.
                   Aventis and ViroPharma shall use Samples strictly in
                   accordance with the then current Commercialization Plan and
                   Budget and shall distribute Samples in full compliance with
                   all applicable Laws, including, without limitation, the
                   requirements of the Prescription Drug Marketing Act of 1987,
                   as amended (the "PDMA"). Each Party, or a Third Party chosen
                   by such Party, shall maintain those records required by the
                   PDMA and all other Laws. ViroPharma shall be solely
                   responsible for filing any necessary reports to FDA in
                   connection with the PDMA.

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          5.13.2  Cost of Samples. The cost per Sample distributed in each
                  Calendar Quarter shall be calculated consistent with the
                  definition of Cost Of Goods.

          5.13.3  Return of Samples. Within thirty (30) days after the
                  termination or expiration of this Agreement for any reason,
                  Aventis shall return, or otherwise dispose of in accordance
                  with instructions from ViroPharma, all remaining Samples and
                  will provide ViroPharma with a certified statement that all
                  remaining Samples have been returned or otherwise properly
                  disposed of and that Aventis is no longer in possession or
                  Control of any such Samples in any form or fashion.

     5.14 Training and Sales Meetings.

          5.14.1  Training of Sales Representatives. Each Party shall be
                  responsible for the training of its own sales representatives
                  at its own costs, in accordance with the training requirements
                  and training programs and using training materials approved by
                  the Marketing Subcommittee, and shall require each of its
                  professional sales representatives to attend sales training
                  for VP Product before their promotion of such VP Product in
                  the Territory. After the initial training meeting, each Party
                  shall periodically provide additional training, in accordance
                  with the training requirements and training programs and using
                  training materials approved by the Marketing Subcommittee, to
                  each of its professional sales representatives promoting VP
                  Product hereunder. At the discretion and upon approval of the
                  Marketing Subcommittee, any such training meetings may be held
                  jointly by the Parties. In any case, either Party may send
                  representatives to observe training provided by the other
                  Party to such other Party's sales representatives.

          5.14.2  Launch Meetings. The Parties shall make reasonable efforts to
                  hold a joint launch meeting for the launch of VP Product.

     5.15 Compliance. In detailing and promoting VP Product in the Territory,
          each Party shall comply and shall cause each of its employees,
          representatives and agents, including, without limitation, each of its
          professional sales representatives, to comply with all Laws and all
          professional requirements including, without limitation, FDA's
          regulations and guidelines concerning the advertising of prescription
          drug products, the American Medical Association's Guidelines on Gifts
          to Physicians, the PhRMA Guidelines for Marketing Practices, the ACCME
          Standards for Commercial Support of Continuing Medical Education, and
          the then current Commercialization Plan and Budget for VP Product.
          Neither Party shall do anything that such Party knows or reasonably
          should know would jeopardize the goodwill or reputation of either
          Party or the reputation of VP Product.

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                                                                         Page 51
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     5.16  Commercialization Trademark Usage Guidelines. Before the Launch Date,
           Aventis and ViroPharma shall consult with SaSy on the adoption of
           guidelines for correct Trademark usage (the "Guidelines"). The final
           content of the Guidelines shall be at the discretion of SaSy.
           ViroPharma and Aventis shall conform to the Guidelines in using the
           Trademarks. Upon SaSy's request, such request not to be made more
           than two times in any Calendar Year, or if ViroPharma and Aventis
           propose to use the Trademarks other than in conformance with the
           Guidelines, ViroPharma shall submit to SaSy samples of any
           Promotional Materials, labels or labeling bearing the Trademarks.
           Upon notification by SaSy within fifteen (15) days after SaSy's
           receipt of such samples of any improper usage of Trademarks therein,
           ViroPharma and Aventis shall make reasonable modifications to correct
           such improper Trademark usage. Following such modifications, or if
           SaSy has not issued a notification as provided above, ViroPharma and
           Aventis may use such Promotional Materials, labels or labeling in
           connection with VP Product, and may modify the same provided that
           there is no change in the usage of the Trademark. The Parties
           acknowledge that SaSy owns the Trademarks and that SaSy may require
           modifications to packaging and promotional materials to the extent
           necessary to ensure Trademark usage in accordance with the
           Guidelines. All use by ViroPharma and Aventis of the Trademark shall
           inure solely to SaSy.

     5.17  Combination Products. The Parties acknowledge that the development
           and/or commercialization of a Combination Product is subject to the
           prior approval of SaSy under the SaSy Agreement. If the Parties
           desire to develop and/or commercialize a Combination Product,
           ViroPharma agrees to use commercially reasonable efforts to obtain
           the consent of SaSy to such development and/or commercialization by
           ViroPharma and Aventis under this Agreement.

6.   VP PRODUCT SUPPLY.

     6.1   Supply of VP Product, Pursuant to the terms of this Agreement:

           6.1.1  ViroPharma agrees to have manufactured and packaged Finished
                  VP Product for sale and Distribution by Aventis and sampling
                  by the Parties in the Territory in such quantities as is equal
                  to actual orders of Finished VP Product accepted by ViroPharma
                  or a Product Supplier for Finished VP Product, and

           6.1.2  Aventis agrees to purchase for sale, sampling and Distribution
                  in the Territory from ViroPharma, or a Product Supplier(s) for
                  Finished VP Product, such quantities of Finished VP Product.

     6.2   Special Provisions to Apply During the Initial Supply Period. This
           provision 6.2 shall apply during the Initial Supply Period only and
           this Section 6.2 shall cease to have effect after the Initial Supply
           Period:

           6.2.1  Firm Orders Before and After the Launch Date.

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                                                                         Page 52
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          (a)  Before and after the Launch Date approved by the JSC, at least
               five (5) days before the first day of each month, Aventis shall
               order from Product Supplier(s) of Finished VP Product or from
               ViroPharma, as applicable, Finished VP Product (by SKU) for
               delivery to Aventis by the end of the second month after such
               month (i.e., three (3) months and five (5) days after such
                      ----
               order), or such later date as is specified by Aventis (each such
               order, an "Order"), but in the case of Orders made before the
               Launch Date, in no event for delivery before the later of (i) the
               Launch Date, and (ii) the date four (4) weeks after the date of
               Regulatory Approval by the FDA of such VP Product. For the sake
               of clarity, except as set forth in Section 6.2.3, Aventis shall
               only be obligated to accept Finished VP Product.

          (b)  ViroPharma shall, or shall cause its Product Supplier of Finished
               VP Product to, accept, or reject, as permitted in this Section
               6.2.1, within five (5) business days any Order received from
               Aventis and shall, or shall cause its Product Supplier of
               Finished VP Product, to accept any Order for a number of units of
               Finished VP Product up to ****** per cent (******%) of the number
               of units of Finished VP Product forecasted in the short term
               forecast to be delivered in the month of delivery, ******
               (******) ****** prior to the date of delivery of such Order (the
               "Maximum Order"). (For example, if in January the MSC forecasts a
               required delivery of 100 units in ******, then the total of Firm
               Orders for ****** placed five (5) days before ****** shall not
               obligate ViroPharma to deliver more than ****** units by the end
               of ******.) ViroPharma shall, or shall cause its Product Supplier
               of Finished VP Product to, exert commercially reasonable efforts
               to supply such quantities ordered by Aventis, which exceed the
               Maximum Order. However ViroPharma or its designated Product
               Supplier of Finished VP Product shall not be obligated to fulfill
               such orders in excess of the Maximum Order by drawing down from
               the ViroPharma safety stock of VP Compound, unless the SCSC
               agrees thereto. The number of units ordered up to and including
               the Maximum Order and, to the extent accepted by ViroPharma, any
               number of units ordered in excess of the Maximum Order, shall be
               a "Firm Order".

          (c)  Notwithstanding any other provisions of this Agreement,
               ViroPharma shall not be obligated to accept Orders, including
               Maximum Orders, for or supply quantities of Finished VP Product
               in excess of the maximum amounts contractually required to be
               manufactured by Product Suppliers of VP Compound, VP Product or
               Finished VP Product.

   6.2.2  Supply Failure.

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                                                                         Page 53
<PAGE>

          (a)  Failure.

               (i)   ****** Supply Failure. If for any ****** (******) ****** in
                     any ****** (******) ****** the number of units (SKU) of
                     Finished VP Product delivered in each of such ****** is
                     less than ****** percent (******%) of the number of units
                     (SKU) in each Firm Order to be delivered in each such
                     ******, then ViroPharma shall ****** after such ******
                     (******) ******, in which the amount of VP Product
                     delivered ****** is less than ****** percent (******%) of
                     the amount of the Firm Order to be delivered ******.

               (ii)  ****** Supply Failure. If for any ****** (******) ******
                     the number of units of Finished VP Product delivered in
                     each of such ****** is less than ****** percent (******%)
                     of the number of units (SKU) in each Firm Order to be
                     delivered in such ****** then ViroPharma shall ****** after
                     such ****** (******) ****** in which the amount of VP
                     Product delivered in ****** is less than ****** percent
                     (******%) of the amount of the Firm Order to be delivered
                     ******, but only until such failure is remedied as set
                     forth in Section 6.2.2(b).

               (iii) ******. ViroPharma shall be required to make no more ******
                     under this Section 6.2.2(a) in any ******, and such ******.
                     ViroPharma shall ****** such ****** within ****** for which
                     ******.

          (b)  Remedy of ****** Supply Failure. A supply failure of the type
               described in Section 6.2.2(a)(ii) shall be remedied after
               ******(******) ****** in which the amount of VP Product delivered
               is ****** percent (******%) or more of the units (SKU) ordered in
               Firm Orders to be delivered in each of such ******, and this
               Section 6.2.2 shall cease to be in effect, until such time as
               another Supply Failure occurs.

    6.2.3 Purchase of Launch Stocks of VP Product. At any time after December
          31, 2001, but prior to the Launch Date for the First Indication as
          approved by the JSC, at ViroPharma's written request, Aventis shall
          purchase from ViroPharma up to such amounts of VP Product in finished
          packaged form ready for sale or sampling and distribution in the
          Territory by Aventis, but without the product information insert or
          outsert, which VP Product results from nine (9) batches of VP
          Compound, each batch being approximately ****** (******) kg (the
          "Aventis Launch Batches"), at the Cost of Goods (excluding the
          validation costs) for such VP Product.

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                                                                         Page 54
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          Either a Product Supplier agreed to by ViroPharma and Aventis, or
          Aventis, at its option, shall attach to or insert into such VP Product
          any product information insert or outsert for such VP Product before
          the Launch Date, subject to the overall rework coordination of
          ViroPharma. The costs of such activity shall be charged to the
          Commercialization Account of either Party, as applicable. ViroPharma
          shall take, promptly after the Effective Date, those actions necessary
          to permit Aventis to perform the activities described in this Section
          6.2.3, including without limitation, listing Aventis in the NDA for
          such VP Product.

   6.2.4  Return of Aventis Launch Batches.  If

          (a)  at any time before the Launch Date, (i) the remaining period of
               time before the expiration date of the VP Product in the Aventis
               Launch Batches is less than ****** (******) ******, or (ii) the
               remaining period of time before the expiration date of any
               Samples of VP Product in the Aventis Launch Batches is less than
               ****** (******) ******, or

          (b)  after the Launch Date, Aventis is not able to (i) sell the VP
               Product in the Aventis Launch Batches before the remaining period
               of time before the expiration date of the VP Product in the
               Aventis Launch Batches is less than ****** (******) ******, or
               (ii) distribute Samples of VP Product in the Aventis Launch
               Batches before the date which is ****** (******) ******before the
               expiration date of such VP Product,

          then ViroPharma shall at Aventis' request, repurchase from Aventis
          such VP Product or Samples of such VP Product at ******, and shall pay
          for such repurchased VP Product or Samples of VP Product within thirty
          (30) days after the later of receipt or invoicing. ViroPharma shall
          bear the cost of destruction or return of such VP Product or Samples
          of such VP Product. None of the amounts expended by ViroPharma
          pursuant to this Section 6.2.4 shall be charged to ViroPharma's
          Commercialization Account.

   6.2.5  Shelf Life. During the Initial Supply Period, ViroPharma shall bear
          all costs associated with Finished VP Product and Samples of Finished
          VP Product rejected by Aventis pursuant to Section 6.4.2, and shall
          not charge such costs to its Commercialization Account.

   6.2.6  Product Suppliers.

          (a)  To the extent permitted under a contract of ViroPharma (or any of
               its Affiliates) with a Product Supplier or as expressly agreed to
               by the Product Supplier, Aventis shall be invited to attend all
               material

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                                                                         Page 55
<PAGE>

               meetings, audits and inspections between ViroPharma and such
               Product Supplier.

          (b)  Without the prior written consent of Aventis, ViroPharma shall
               not:

               (i)   Make any election or exercise any right or option to
                     terminate in whole or in part any agreement with a
                     Product Supplier; or

               (ii)  Make any election (or fail to elect), exercise any right or
                     option (or fail to so exercise) or give any consent or
                     approval (or fail to give such consent or approval) under
                     any agreement with a Product Supplier which would
                     reasonably be expected to result in an increase in the Cost
                     of Goods of any VP Product.

     6.3  After Initial Supply Period.  After the Initial Supply Period, unless
          otherwise provided for herein,

          6.3.1 the Parties will collaborate on the management of the supply
                chain of VP Compound, VP Product and Finished VP Product,

          6.3.2 Aventis shall order from the Product Supplier of Finished VP
                Product such number of units of Finished VP Product as
                determined by the SCSC,

          6.3.3 ViroPharma shall order such amounts of VP Compound as determined
                by the SCSC,

          6.3.4 the cost of any Finished VP Product rejected by Aventis under
                Section 6.4.2 shall be shared as a Commercialization Expense,
                but only to the extent that Section 6.4.12 does not apply,

          6.3.5 only if the SCSC instructs ViroPharma to manufacture a certain
                amount of VP Compound and VP Product, and if such amount of VP
                Compound or VP Product, which was usable at the time of its
                receipt by or on behalf of ViroPharma, becomes unusable before
                it is converted into Finished VP Product, other than because of
                loss or damage, then upon the date that such amount of VP
                Compound or VP Product becomes unusable, ViroPharma shall be
                permitted to charge the cost of such amount of VP Compound or VP
                Product to its Commercialization Account,

          6.3.6 the Parties shall share as a Commercialization Expense, the
                risks and associated costs of any decisions made unanimously by
                the SCSC,

          To the extent any issue regarding the supply chain of VP Compound, VP
          Product and Finished VP Product is not specifically addressed in this
          Agreement, the

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                                                                         Page 56
<PAGE>
          SCSC shall collaborate to address and resolve such issue in a
          reasonable and adequate manner.

     6.4  General Provisions to Apply Throughout the Term of this Agreement. The
          provisions of this Section 6.4 shall apply throughout the term of this
          Agreement:

          6.4.1   Generally. Aventis shall make payments to Product Supplier(s)
                  of Finished VP Product, or ViroPharma, as applicable, in U.S.
                  dollars within thirty (30) days after the later of receipt of
                  Finished VP Product or invoicing for such Finished VP Product,
                  and shall have the sole right and responsibility to hold all
                  inventory of such Finished VP Product. Aventis shall charge
                  all payments for Finished VP Product or VP Product of the
                  Aventis Launch Batches and/or Cost of Goods to its
                  Commercialization Account when such Finished VP Product or VP
                  Product of the Aventis Launch Batches is sold to Third
                  Parties.

          6.4.2   Shelf Life. Aventis shall be entitled to reject any Finished
                  VP Product for which the remaining period of time before the
                  expiration date for such Finished VP Product on the date of
                  receipt by Aventis of such Finished VP Product is (a) less
                  than ****** (******) ****** if the Shelf Life for such VP
                  Product is at least ****** (******) ******, or (b) less than
                  ****** (******) ****** if the Shelf Life for such Finished VP
                  Product is at least ****** (******) ******. Aventis shall
                  notify ViroPharma of its decision to reject or accept Finished
                  VP Product as provided for in this Section 6.4.2 within ten
                  (10) business days from receipt of such Finished VP Product.
                  If Aventis fails to notify ViroPharma of any such rejection
                  within such ten (10) business days, Aventis shall be deemed to
                  have accepted such Finished VP Product.

          6.4.3   Invoicing. The Product Supplier of Finished VP Product or
                  ViroPharma, as applicable, shall invoice Aventis for the full
                  Cost of Goods of Finished VP Product ordered by Aventis
                  pursuant to Article 6.

          6.4.4   Title and Risk of Loss. Title to, and risk of physical loss of
                  or damage to Finished VP Product or VP Product in the Aventis
                  Launch Batches shall pass to Aventis upon acceptance of tender
                  of delivery of such Finished VP Product or VP Product in the
                  Aventis Launch Batches to Aventis' facility or to any Third
                  Party's facility designated by Aventis. Title to, and risk of
                  physical loss of or damage to Finished VP Product or VP
                  Product in the Aventis Launch Batches shall remain with
                  ViroPharma before acceptance of tender of delivery of such
                  Finished VP Product or VP Product in the Aventis Launch
                  Batches to Aventis' facility or to any Third Party's facility
                  designated by Aventis. Any costs associated with physical loss
                  of or damage to Finished VP Product or VP Product in the
                  Aventis Launch Batches shall not be charged to either Party's
                  Commercialization Account.

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     6.4.5  Receipt. Within five (5) days of receiving any shipment of VP
            Product, Aventis shall inventory such shipment and confirm the
            receipt of VP Product in the Aventis Launch Batches, and the amount
            of Finished VP Product ordered in a Firm Order. Aventis shall
            promptly notify ViroPharma of any discrepancies.

     6.4.6  Release. ViroPharma shall be solely responsible for releasing
            Finished VP Product to the market. ViroPharma shall perform or have
            performed on ViroPharma's behalf any release testing on any Finished
            VP Product or VP Product of Aventis Launch Batches and shall release
            such Finished VP Product or VP Product of Aventis Launch Batches
            prior to shipment to Aventis.

     6.4.7  Suppliers

            (a)  Selection of Suppliers. The SCSC shall, without unreasonable
                 delay after the Effective Date, agree on the criteria for the
                 selection and qualification of Product Suppliers. On the basis
                 of such criteria the SCSC shall recommend to the JSC for
                 approval any Product Suppliers needed after the Effective Date
                 in addition to the suppliers listed in Exhibit 6.4.7(a)
                 attached hereto. All other decisions and actions to be taken
                 concerning Product Suppliers shall be made by the SCSC and no
                 Party shall take any unilateral actions with respect to any
                 such Product Supplier except as determined by the SCSC, and
                 except during the Initial Supply Period. ViroPharma shall
                 provide Aventis with copies of all draft agreements with
                 Product Suppliers for prompt review and comment by Aventis.
                 Notwithstanding anything to the contrary in this Section
                 6.4.7(a), ViroPharma shall be permitted unilaterally to enter
                 into an agreement with a Product Supplier listed in Exhibit
                 6.4.7(a), provided that ViroPharma makes good faith efforts to
                 incorporate reasonable comments provided by Aventis to
                 ViroPharma. ViroPharma may not become a manufacturer of VP
                 Compound, VP Product, or Finished VP Product without the prior
                 written approval of Aventis.

            (b)  Qualification of Suppliers. At the direction of the SCSC,
                 ViroPharma, and Aventis if Aventis so desires and to the extent
                 consistent with Aventis' rights under this Agreement, shall
                 enter into supply agreements with Product Suppliers. At the
                 direction of the SCSC, ViroPharma shall be solely responsible
                 for transferring technology to such Product Suppliers, and for
                 obtaining any necessary Regulatory Approval by the FDA for the
                 use of such Product Suppliers.

            (c)  Product Supplier Breach. If either Party believes that a
                 Product Supplier has breached any term of its agreement to
                 supply VP

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                                                                         Page 58
<PAGE>

                 Compound, VP Product or Finished VP Product, the Party shall
                 promptly notify the SCSC. The SCSC shall consider whether to
                 take any action to enforce any rights under such agreement. At
                 the direction of the SCSC, ViroPharma shall use commercially
                 reasonable efforts to enforce such agreement. The Parties shall
                 share equally the costs of any activities under this Section
                 6.4.7(c) and any amounts received from Third Parties as a
                 result of such activities.

     6.4.8   Finished VP Product Supplier Liaison and Ordering. Consistent with
             Sections 6.2 and 6.3, Aventis shall order Finished VP Product from
             a Product Supplier of Finished VP Product, except that, if
             otherwise required, ViroPharma shall transmit such orders from
             Aventis to a Product Supplier of Finished VP Product, and
             ViroPharma shall be the liaison between the Parties and the Product
             Supplier.

     6.4.9   VP Compound Supplier Liaison. Consistent with Sections 6.2 and 6.3,
             ViroPharma shall order VP Compound as required to fulfill Aventis'
             orders of Finished VP Product.

     6.4.10  Long-Term Forecasting. At least ninety (90) days prior to the
             beginning of each Calendar Year (other than the Calendar Year
             covering the period of time from the Effective Date through
             December 31, 2001), the MSC shall submit to the JSC for approval a
             forecast by Calendar Quarters of the quantities of Finished VP
             Product (by SKU) that are needed to support the applicable
             Commercialization Plan and Budget for each Calendar Quarter during
             the three (3) Calendar Years period commencing with the upcoming
             Calendar Year (or, if shorter, the remainder of the term of this
             Agreement), for the Territory. Such forecasts shall be provided to
             the SCSC. The Parties acknowledge that such long-term forecasts
             shall represent reasonable good faith estimates for planning
             purposes, but shall not be used for purchase or supply commitments.

     6.4.11  Short-Term Forecasting. On a monthly basis, the MSC shall prepare a
             rolling monthly forecast, of the quantities of VP Product (by SKU)
             that are needed to support the applicable Commercialization Plan
             and Budget for each month during the following twenty-four (24)
             month period (or, if shorter, the remainder of the term of this
             Agreement), for the Territory. Such forecasts shall be provided to
             the SCSC.

     6.4.12  Limitation on Charges to Commercialization Account of VP Product.
             Except as provided in Section 6.3.5, any inventory of VP Compound,
             VP Product or Finished VP Product held by ViroPharma shall be
             included in Cost of Goods only to the extent that it is converted
             into Finished VP Product and delivered to and accepted by Aventis,
             and only in accordance with the definition of Cost of Goods, and
             only then may it be charged to a Commercialization Account.

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     6.4.13  Repackaging and Relabeling. Notwithstanding anything to the contrar
             in this Agreement, Aventis shall have no right to repackage or
             relabel any VP Product without the prior written consent of
             ViroPharma or except as otherwise provided in Section 6.2.3.

     6.4.14  Aventis' Option to Supply. At any time during the term of this
             Agreement, if Aventis makes an offer on commercially reasonable
             terms to become a Product Supplier, ViroPharma agrees to negotiate
             in good faith to permit Aventis to become a Product Supplier with
             respect to any or all of the steps required to manufacture VP
             Compound, VP Products or Finished VP Products. ViroPharma shall not
             unreasonably reject Aventis' offer to become a Product Supplier.
             The Parties shall enter into a separate agreement if Aventis is
             chosen to become a Product Supplier, subject to the consent of
             SaSy, and/or shall amend this Agreement to the extent necessary.

     6.4.15  Specifications, Analytical Methods, Testing. Throughout the term of
             this Agreement, ViroPharma shall:

             (a)  develop or have developed (i) product specifications and (ii)
                  analytical test methods for VP Compound, VP product and
                  Finished VP Product,

             (b)  complete or have completed (i) routine stability testing and
                  (ii) product testing and release of VP Compound, VP Product
                  and Finished VP Product and

             (c)  be responsible for product specification change control of VP
                  Compound, VP Product and Finished VP Product.

     6.4.16  Aventis Costs. The reasonable internal personnel cost and
             associated out-of-pocket cost incurred by Aventis to complete
             assessments of the Product Suppliers listed in Exhibit 6.4.7(a) and
             to become familiar with the manufacturing processes, product
             specifications, and laboratory procedures of VP Compound, VP
             Product and Finished VP Product shall be charged to Aventis'
             Commercialization Account, and the JSC shall be deemed to have
             agreed to such charges.

     6.4.17  Costs of Rejected Finished VP Product. The cost of Finished VP
             Product properly rejected by Aventis because such Finished VP
             Products does not conform to ViroPharma's representations and
             warranties in Section 14.2.1(a-c).

     6.4.18  Costs of Supply Chain Management. Either Party shall charge the
             reasonable out-of-pocket cost incurred by such parties for
             activities required for the joint management of the supply chain as
             provided for in Section 6.3, to the extent approved by the SCSC.

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7.   REGULATORY MATTERS.

     7.1  Communication with Regulatory Authorities.

          7.1.1  General. ViroPharma shall consult with Aventis through the
                 Development Subcommittee on the regulatory strategy to be
                 pursued for VP Compounds and VP Products. ViroPharma shall be
                 solely responsible for maintaining and seeking in its own name
                 Regulatory Approvals for VP Product, including all NDAs and all
                 additional or supplemental Regulatory Approvals, provided any
                 filings for Regulatory Approvals submitted after the Effective
                 Date are not inconsistent with the decisions of the Joint
                 Steering Committee or its subcommittees. ViroPharma shall be
                 solely responsible for filing all reports required to be filed
                 in order to maintain any Regulatory Approvals granted for VP
                 Product, including, without limitation, Adverse Drug Experience
                 reports. ViroPharma shall not make any submissions to any
                 Regulatory Authority concerning an NDA that are intended to
                 materially change or modify the label or labeling for, or the
                 indication of VP Product without first notifying and obtaining
                 the input of the full DSC. ViroPharma shall not make any
                 material submissions to any Regulatory Authority of an NDA, or
                 concerning an NDA, for VP Product for an Other Indication
                 without the approval of the JSC. At least thirty (30) days
                 before making any material submission to any Regulatory
                 Authority of an NDA, or concerning any NDA, for VP Product for
                 the Second Indication or any Additional Indication, ViroPharma
                 shall provide the JSC with a copy of such submission, and
                 ViroPharma shall adopt reasonable suggestions made by the JSC
                 to the extent feasible. Aventis shall cooperate with ViroPharma
                 as needed in preparing and filing all such reports and, upon
                 ViroPharma's request, provide ViroPharma with any information
                 in Aventis' possession or control that ViroPharma reasonably
                 deems to be relevant to any such reports.

          7.1.2  ViroPharma Notification of Significant Regulatory Information.
                 ViroPharma shall promptly notify the Aventis members of the DSC
                 as soon as material information and data generated in the
                 course of the development program become available to
                 ViroPharma. ViroPharma will promptly provide the members of the
                 DSC with all such material information and data in order to
                 evaluate this progress in the development program.

          7.1.3  Aventis Meeting Attendance. Consistent with Laws, Aventis shall
                 have the right to have up to three (3) of its representatives
                 attend all meetings and conferences and participate in all
                 material telephone discussions with any Regulatory Authority in
                 the Territory concerning VP Compounds or VP Products.
                 ViroPharma shall promptly provide Aventis' members on the DSC
                 with copies of all correspondence between ViroPharma and a
                 Regulatory Authority regarding VP Products or VP Compound, or
                 regarding the activities under this Agreement at least seven
                 (7) days before

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                 the submission of such correspondence, to the extent reasonably
                 feasible. ViroPharma shall adopt all reasonable material
                 suggestions and recommendations of Aventis concerning such
                 correspondence, to the extent feasible.

          7.1.4  Inspections & Inquiries. If either Party or any of their
                 respective Affiliates is inspected by or receives inquiries
                 from a Regulatory Authority regarding activities under this
                 Agreement with regard to VP Compound, VP Product, or Finished
                 VP Product, such Party or the applicable Affiliate shall
                 promptly notify the other Party, but in no event more than
                 forty-eight (48) hours after such inspection or inquiry. The
                 inspected Party or its Affiliate shall provide the other Party
                 with a written report of any such inspection, noting with
                 specificity any record or document reviewed by the regulatory
                 inspector. When a copy of a document or record is supplied to
                 the inspector on request, that fact will be noted in the
                 report. The inspected Party or its Affiliate shall keep copies
                 of each of these records or documents in a separate inspection
                 file and, on the other Party's request, will provide such other
                 Party with copies of any or all of these documents or records.

          7.1.5  Aventis Communications with Regulatory Authorities. If Aventis
                 reasonably concludes, after consultation with its regulatory
                 counsel, that Aventis must communicate with a Regulatory
                 Authority regarding Aventis' activities under this Agreement,
                 then Aventis shall so advise ViroPharma, and provide ViroPharma
                 with copies of all correspondence between Aventis and the
                 Regulatory Authority. Aventis shall provide ViroPharma with
                 copies of all correspondence, documents and materials received
                 from a Regulatory Authority concerning VP Compounds, VP
                 Products or any activities under this Agreement. Aventis shall
                 provide ViroPharma with copies of any proposed correspondence
                 to a Regulatory Authority that relates to VP Compounds, VP
                 Products, or any activities under this Agreement at least seven
                 days before the submission of such correspondence. Aventis
                 shall adopt all reasonable suggestions and recommendations of
                 ViroPharma concerning any meeting or written or oral
                 communication with such Regulatory Authority.

     7.2  Regulatory Cooperation.

          7.2.1  Each Party shall provide the other with all reasonable
                 assistance and take all actions reasonably needed to enable
                 such other Party to comply with any Law applicable to such
                 other Party's activities under this Agreement. Such assistance
                 and actions shall include, without limitation, informing the
                 other Party within forty-eight (48) hours of receiving any
                 information that:

                 (a)  raises any material concerns regarding the safety or
                      efficacy of any VP Product;

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                                                                         Page 62
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                  (b)  indicates or suggests a potential material liability for
                       either Party to Third Parties arising in connection with
                       any VP Product;

                  (c)  is reasonably likely to lead to a recall or market
                       withdrawal of any VP Product; or

                  (d)  concerns any ongoing or potential investigation,
                       detention, seizure or injunction involving any VP Product
                       by any Regulatory Authority,

                  including, without limitation, receipt of a warning letter
                  relating to any VP Compounds or VP Products; and an initiation
                  of any governmental or regulatory authority investigation,
                  detention, seizure or injunction concerning any VP Compound or
                  VP Product.

          7.2.2   ViroPharma shall have the sole right and responsibility to
                  determine whether subsequent notification to a Regulatory
                  Authority is required, and to provide such notification to the
                  Regulatory Authority in compliance with Law.

          7.2.3   To the extent consistent with the Commercialization Plan and
                  Budget and the Development Plan and Budget, ViroPharma shall
                  apply for and maintain the NDA and all other Regulatory
                  Approvals necessary to promote, Detail and Distribute VP
                  Products.

     7.3  Labeling and Promotional Materials. ViroPharma shall be solely
          responsible for obtaining any approval from a Regulatory Authority of
          any label, labeling, package inserts, packaging, and Promotional
          Materials used in connection with VP Product, and for determining
          whether the same requires approval from a Regulatory Authority.
          ViroPharma shall use commercially reasonable efforts to establish and
          maintain the resources to perform its duties under this Section 7.3.
          As permitted by applicable Laws, ViroPharma and Aventis shall be given
          equal exposure and prominence on all VP Product labels, labeling,
          package inserts, packaging, and Promotional Materials used or
          distributed in connection with VP Product under this Agreement; except
          that either Party may request that its name not be used, to the extent
          permitted by applicable Laws. As permitted by applicable Laws, the
          Parties shall attempt to have the appearance of VP Product labels,
          labeling, package inserts, packaging, and Promotional Materials used
          or distributed in connection with VP Product under this Agreement
          conform with the guidelines and requirements of each Party. Each
          package or label of VP Product shall bear the statement "Under license
          from SANOFI-SYNTHELABO", or such other statement that SaSy may
          reasonably request, including, without limitation, references to
          patent numbers, provided that such wording otherwise complies with all
          Laws applicable to such labeling. ViroPharma shall use commercially
          reasonable efforts to ensure that any markings requested by SaSy to
          appear on the label or packaging of VP Products are reasonable, and
          are consistent with the decisions made by the MSC or the JSC regarding
          such packaging or labeling.

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                                                                         Page 63
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     7.4  Adverse Drug Experiences.

          7.4.1  Notification of Parties.

                 (a)  Serious Adverse Drug Experiences. Each Party shall notify
                      the other of any Serious Adverse Drug Experience within
                      forty-eight (48) hours of the time such Serious Adverse
                      Drug Experience becomes known to such Party or any of its
                      Affiliates, with written confirmation of such notification
                      no more than forty-eight (48) hours later.

                 (b)  Non-Serious Adverse Drug Experiences. Each Party shall
                      notify the other Party in writing of any Non-Serious
                      Adverse Drug Experience within ten (10) days after the end
                      of any Calendar Quarter, listing the Non-Serious Adverse
                      Drug Experience that become known to such Party or any of
                      its Affiliates.

                 (c)  Complaints. Aventis shall refer any complaints, including
                      medical complaints, that it receives concerning any VP
                      Product to ViroPharma within ninety-six (96) hours of
                      receiving such complaint; provided that all complaints
                      concerning suspected or actual VP Product tampering,
                      contamination or any VP Product that is out-of-
                      specification shall be delivered within forty-eight (48)
                      hours of receiving such Complaint.

          7.4.2  Notification of SaSy. ViroPharma shall provide SaSy with all
                 data and information about Adverse Drug Experiences and
                 complaints related to VP Product as soon as such data and
                 information are available, and Aventis shall assist in
                 providing such data and information to the extent necessary.

          7.4.3  Regulatory Reporting. ViroPharma shall be responsible for
                 making all reports to any Regulatory Authority regarding
                 Adverse Drug Experiences.

          7.4.4  Disclosure. Except as required by applicable Laws, Aventis
                 shall not disclose any information concerning any Adverse Drug
                 Experience or any complaint concerning any VP Product to any
                 Third Party without the prior consent of ViroPharma. ViroPharma
                 shall be solely responsible for determining whether any
                 complaint or Adverse Drug Experience must be reported to any
                 Regulatory Authority and to provide such notification in
                 compliance with applicable Laws.

          7.4.5  Sharing of Information. Within five (5) days of submission,
                 ViroPharma shall provide Aventis with a copy of any 15 day
                 "Alert Reports" relating to any VP Product submitted to FDA in
                 accordance with 21 C.F.R. (S) 314.80(c)(1) and any periodic
                 adverse drug experience report relating to any VP Product
                 submitted in accordance with 21 C.F.R. (S) 314.80(c)(2).

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          7.4.6  Additional Agreements. The Parties shall enter into such
                 additional agreements governing the sharing and reporting of
                 data and information on adverse drug experiences and complaints
                 related to VP Product as the JSC deems necessary.

     7.5  Recalls or Other Corrective Action of VP Product. ViroPharma shall be
          solely responsible for and shall make any final decisions with respect
          to any recall, market withdrawals or any other corrective action
          related to VP Product in the Territory. Before making any such recall
          decision, to the extent possible ViroPharma shall notify and consult
          with Aventis. ViroPharma shall promptly notify Aventis of any such
          actions planned to be taken by ViroPharma that are reasonably likely
          to materially and adversely affect the marketability of VP Products in
          the Territory or could be reasonably foreseen to materially damage or
          materially adversely affect Aventis' reputation as a pharmaceutical
          company. In the event of any such proposed actions, Aventis shall have
          the right to review and comment upon such proposed actions and, if
          appropriate, participate in any statements to the extent feasible
          under the circumstances. At ViroPharma's request, Aventis shall
          provide reasonable assistance to ViroPharma in conducting such recall,
          market withdrawal or other corrective action, including, without
          limitation, providing all of Aventis' pertinent records that
          ViroPharma may reasonably request to assist in effecting such recall,
          marketing withdrawal or other corrective action.

     7.6  Cost of Recalls or Other Corrective Actions. Except as expressly
          otherwise provided below in this Section 7.6, the Parties shall share
          equally all costs of a recall, marketing withdrawal or other
          corrective action of a VP Product in the Territory. Notwithstanding
          the foregoing, a Party shall bear any and all costs of a recall,
          market withdrawal or other corrective action of a Finished VP Product
          in the Territory to the extent such recall, market withdrawal or other
          corrective action results solely from:

          7.6.1  in the case of ViroPharma:

                 (a)  a negligent or reckless act or omission or intentional
                      misconduct on the part of ViroPharma, its Affiliates or
                      contractors and not from a negligent or reckless act or
                      omission or intentional misconduct on the part of Aventis,
                      its Affiliates or contractors,

                 (b)  the failure of a VP Compound or VP Product to be
                      manufactured in compliance with all Laws and in accordance
                      with its applicable specifications,

                 (c)  the failure of a VP Product or VP Compound to be held and
                      shipped in compliance with all Laws and in accordance with
                      its applicable specifications before its delivery to
                      Aventis pursuant to Section 6.4.4,

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                                                                         Page 65
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                 (d)  the failure of ViroPharma to comply with any Law in
                      connection with its responsibilities under this Agreement;
                      and

          7.6.2  in the case of Aventis:

                 (a)  a negligent or reckless act or omission or intentional
                      misconduct on the part of Aventis, its Affiliates or
                      contractors and not from a negligent or reckless act or
                      omission or intentional misconduct on the part of
                      ViroPharma, its Affiliates or contractors,

                 (b)  the failure of a VP Compound or VP Product manufactured by
                      Aventis to be manufactured in compliance with all Laws and
                      in accordance with its applicable specifications, if and
                      to the extent that Aventis in fact manufactures VP
                      Product,

                 (c)  the failure of a VP Product to be held, shipped or
                      Distributed in compliance with all Laws and in accordance
                      with its applicable specifications, from and after its
                      delivery to Aventis pursuant to Section 6.4.4,

                 (d)  the failure of Aventis to comply with any Law in
                      connection with its responsibilities under this Agreement.

          A Party shall have no obligation to reimburse or otherwise compensate
          the other Party for any lost profits or income that may arise in
          connection with any such recall or market withdrawal.

     7.7  Medical Inquiries. ViroPharma shall be solely responsible for
          responding to medical questions or inquiries from members of the
          medical and paramedical professions and consumers regarding VP
          Product, either itself, through a Third Party contractor, or, subject
          to the agreement of Aventis, through a contract with Aventis to
          perform such activities. Aventis shall refer all such questions about
          VP Product that it receives to ViroPharma, unless Aventis has been
          made responsible for performing such activities with the Agreement of
          the JSC.

8.   CONSIDERATION, PROFIT & COST SHARING.

     8.1  Aventis Milestone Payments. In consideration for the rights granted to
          Aventis under this Agreement, Aventis shall pay ViroPharma the
          following amounts:

          8.1.1  Signing. Twenty-five million U.S. dollars (U.S. $25,000,000.00)
                 upon the signing of this Agreement, the following amounts of
                 which shall be refunded by ViroPharma to Aventis as follows:

                 (a)  ****** U.S. dollars (U.S. $******) if Regulatory Approval
                      of an NDA for VP Product for the First Indication has not
                      been granted in the United States by ******; and

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                 (b)  ****** U.S. dollars (U.S. $******) if Regulatory Approval
                      of an NDA for VP Product for the First Indication has not
                      been granted in the United States by ******.

                 If before the first Regulatory Approval in the United States of
                 an NDA for VP Product for the First Indication, ViroPharma's
                 ****** U.S. dollars ($******), ViroPharma shall ****** U.S.
                 dollars (U.S. $******) ******, and ****** U.S. dollars (U.S.
                 $******) ******.

          8.1.2  First Indication. ****** U.S. dollars ($******) upon the first
                 Regulatory Approval in the United States of an NDA for VP
                 Product for the First Indication ****** for the First
                 Indication ******:

                 (a)  ******, except that this Section 8.1.2(a) shall not apply
                      if, on the date of Regulatory Approval of the respective
                      indication, ******; or

                 (b)  ****** or ******; or

                 (c)  ******:

                      (i)  ******, or

                      (ii)  ******;

                 (collectively, "******").

          8.1.3  Second Indication Subset.

                 (a)  General. Upon the Regulatory Approval in the United States
                      of an NDA for VP Product that includes the Second
                      Indication Subset:

                      (i)  ****** U.S. dollars (U.S. $******) if such Regulatory
                           Approval is obtained on or before ******; or

                      (ii) ****** U.S. dollars (U.S. $******) if such Regulatory
                           Approval is obtained after ****** but on or before
                           ******.

                 (b)  Exceptions. No payment shall be due under Section 8.1.3(a)
                      if:

                      (i)  the ****** for such VP Product for the Second
                           Indication Subset ****** that such VP Product is
                           indicated for the Second Indication Subset ******,
                           and on the date of Regulatory Approval of the Second
                           Indication that includes the Second Indication
                           Subset, ******, or

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                      (ii) Regulatory Approval in the United States of an NDA
                           for VP Product for the Second Indication Subset is
                           obtained after ******.

               8.1.4  Labeling - Otitis Media. ****** U.S. dollars (U.S.
                      $******) upon the first Regulatory Approval in the United
                      States of an NDA for VP Product for which the labeling
                      contains a positive description of the efficacy of such VP
                      Product with respect to Otitis Media that can be promoted
                      by a sales representative in accordance with the FD&C Act,
                      and for which VP Product the ****** regarding Otitis Media
                      ******.

               8.1.5  Additional Indication - Asthma. ****** U.S. dollars (U.S.
                      $******) upon the first Regulatory Approval in the United
                      States of an NDA for VP Product for the Asthma Indication,
                      for which VP Product ******. If the first Regulatory
                      Approval for such VP Product for such Additional
                      Indication is obtained after ******, the amount to be paid
                      by Aventis under this Section 8.1.5 ****** (the "******"):

                          Calendar Year During Which    ******
                          Regulatory Approval of VP     to be Paid by Aventis to
                          Product for Additional        ViroPharma
                          Indication Is Obtained        ------------------------
                          --------------------------
                                   ******                         ******
                                   ******                         ******
                                   ******                         ******
                                   ******                         ******

               8.1.6  Additional Indication - COPD. ****** U.S. dollars (U.S.
                      $******) upon the first Regulatory Approval in the United
                      States of an NDA for VP Product for the COPD Indication,
                      ******. If the first Regulatory Approval for such VP
                      Product for such Additional Indication is obtained after
                      ******, the amount to be paid by Aventis under this
                      Section 8.1.6 ****** (the "******"):

                          Calendar Year During Which    ******
                          Regulatory Approval of VP     to be Paid by Aventis to
                          Product for Additional        ViroPharma
                          Indication Is Obtained        ------------------------
                          --------------------------
                                   ******                         ******
                                   ******                         ******
                                   ******                         ******
                                   ******                         ******

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          8.1.7  Other Indications. ****** U.S. dollars (U.S. $******) upon the
                 first Regulatory Approval of an NDA for each Other Indication
                 for which:

                 (a)  ******,

                 (b)  Aventis has chosen to ******, as such Other Indication has
                      been defined by the Development Committee in the
                      Development Plan and Budget as set forth in Section
                      4.4.2(e), and

                 (c)  the development of such Other Indication was approved by
                      the JSC.

          8.1.8  Sales Level Payments.

                 (a)  Net Sales - $******. One time payment of ****** U.S.
                      dollars (U.S. $******) upon first achieving Net Sales
                      totaling ****** U.S. dollars ($******) or more in the
                      United States in any twelve (12) consecutive calendar
                      months;

                 (b)  Net Sales - $******. One time payment of ****** U.S.
                      dollars (U.S. $******) upon first achieving Net Sales
                      totaling ****** U.S. dollars ($******) or more in the
                      United States in any twelve (12) consecutive calendar
                      months;

                 (c)  Net Sales - $******. One time payment of ****** U.S.
                      dollars (U.S. $******) upon first achieving Net Sales
                      totaling ****** U.S. dollars ($******) or more in the
                      United States in any twelve (12) consecutive calendar
                      months;

                 (d)  Net Sales - $******. One time payment of ****** U.S.
                      dollars (U.S. $******) upon first achieving Net Sales
                      totaling ****** U.S. dollars ($******) or more in the
                      United States in any twelve (12) consecutive calendar
                      months.

     8.2  Aventis Equity Purchase. On the Effective Date, Aventis or an Aventis
          Affiliate and ViroPharma shall enter into the Stock Purchase Agreement
          attached to this Agreement as Exhibit 8.2.

     8.3  Indication Development Budget Milestones. Upon Regulatory Approval for
          any Additional Indication, or for any Other Indication for which
          Aventis has chosen to ******, as such Other Indication has been
          defined by the Development Committee in the Development Plan and
          Budget as set forth in Section 4.4.2(e), Aventis shall pay ViroPharma
          the Indication Development Budget Milestone for such Additional
          Indication or Other Indication as set forth in Section 4.5.1(b) and
          (c). In the case of an Additional Indication, if the Regulatory
          Approval for such VP Product for such Additional Indication is
          obtained after ******, the amount to be paid by Aventis under this
          Section 8.3 ****** (the "******"):

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          Calendar Year During Which
          Regulatory Approval of VP          ******
          Product for Additional             to be Paid by Aventis to
          Indication Is Obtained             ViroPharma
          -----------------------------      ---------------------------------
                   ******                                   ******
                   ******                                   ******
                   ******                                   ******
                   ******                                   ******
  8.4  Profit Sharing. For so long as the Parties are commercializing any VP
       Product under this Agreement, (a) ViroPharma shall receive forty-five
       percent (45%) of the Net Profits (Losses) obtained from the sale of VP
       Product as a prescription pharmaceutical product, or as an over-the-
       counter pharmaceutical product in the case of either a Forced OTC Switch
       or a Voluntary OTC Switch in a Calendar Quarter in the Territory
       ("ViroPharma's Allocation of Net Profits") and (b) Aventis shall receive
       fifty-five percent (55%) of the Net Profits (Losses) obtained from the
       sale of VP Product as a prescription pharmaceutical product, or as an
       over-the-counter pharmaceutical product in the case of either a Forced
       OTC Switch or a Voluntary OTC Switch in a Calendar Quarter in the
       Territory ("Aventis' Allocation of Net Profits").

  8.5  Profit & Expense Reports and Payments.

       8.5.1  Statements of Estimated Amounts for Purposes of Accruals. No later
              than the last business day of each Calendar Quarter:

              (a)  ViroPharma shall prepare and deliver to Aventis a report for
                   Aventis' internal accounting needs setting forth its good
                   faith estimate of:

                   (i)  Development Expenses incurred or to be incurred by it
                        with respect to a VP Compound or VP Product pursuant to
                        Sections 4.5.1(a) and 4.5.1(c)(i); and

                   (ii) Commercialization Expenses incurred or to be incurred by
                        it with respect to VP Products subject to expense
                        limitations set forth in Section 8.6;

                   in such Calendar Quarter; and

              (b)  Aventis shall prepare and deliver to ViroPharma a report for
                   ViroPharma's internal accounting needs setting forth its good
                   faith estimate of:

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                    (i)   Development Expenses incurred or to be incurred by it
                          with respect to a VP Compound or VP Product pursuant
                          to Sections 4.5.1(a) and 4.5.1(c)(i);

                    (ii)  Commercialization Expenses incurred or to be incurred
                          by it with respect to VP Products subject to expense
                          limitations set forth in Section 8.6,

                    (iii) Net Sales of each VP Product in the Territory achieved
                          or to be achieved in such Calendar Quarter.

     8.5.2     Statement of Actual Accounts. Within forty-five (45) days of the
               end of each Calendar Quarter, each Party shall prepare and
               deliver to the other Party a report setting forth the actual
               amount of each amount reported to the other Party pursuant to
               Section 8.5.1 for such Calendar Quarter. Within twenty-one (21)
               days after the end of the fourth Calendar Quarter, each Party
               will provide a revision of the estimate of the amounts reported
               to the other Party pursuant to Section 8.5.1 for such Calendar
               Quarter, or a confirmation that as of such date no data available
               to such Party require that such estimate be revised.

     8.5.3     Reconciliation. Within sixty (60) days of the end of each
               Calendar Quarter, based on the statements delivered pursuant to
               Section 8.5.2 above, Aventis shall prepare a report setting forth
               the amount of the payment that one Party is required to make to
               the other as follows:

               (a)  the product of ViroPharma's Allocation of Net Profits and
                    the Net Sales of VP Products in the Territory; less
                                                                   ----

               (b)  the product of ViroPharma's Allocation of Net Profits and
                    Commercialization Expenses incurred by Aventis in the
                    Territory; plus
                               ----

               (c)  the product of Aventis' Allocation of Net Profits and
                    Commercialization Expenses incurred by ViroPharma in the
                    Territory; plus
                               ----
               (d)  ****** percent (******%) of Development Expenses incurred by
                    ViroPharma pursuant to Sections 4.5.1(a) and 4.5.1(c)(i);
                    less
                    ----

               (e)  ****** percent (******%) of Development Expenses incurred by
                    Aventis pursuant to Sections 4.5.1(a) and 4.5.1(c)(i).

     8.5.4     Payment. If the amount calculated by Aventis pursuant to Section
               8.5.3 is greater than zero, Aventis shall, within five (5) days
               of its delivery to ViroPharma of the report pursuant to Section
               8.5.3, deliver to ViroPharma

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               a payment in such amount. In the event such amount is less than
               zero, within five (5) days of ViroPharma's receipt of such
               report, ViroPharma shall deliver to Aventis a payment equal to
               the absolute value of such amount.

     8.5.5     SaSy Royalty Reconciliation and Payment. Notwithstanding the
               foregoing Sections 8.5.1 through 8.5.4, no later than fifty-five
               (55) days after the end of each Calendar Quarter, Aventis shall
               send ViroPharma:

               (a)  a report of the amount of the SaSy Royalty due on account of
                    Net Sales of VP Product in such Calendar Quarter in the
                    Territory

               (b)  a statement of the amount of such SaSy Royalty owed by
                    ViroPharma and Aventis respectively as Commercialization
                    Expenses in the Territory,

               (c)  payment to ViroPharma for the full amount of such SaSy
                    Royalty owed by both Parties in readily available U.S.
                    dollars.

               ViroPharma shall be solely responsible for transmitting full
               payment of the SaSy Royalty to SaSy.

8.6  Expense Limitation on Commercialization Expenses. The aggregate
     Commercialization Expenses other than Cost of Goods charged by either Party
     to its Commercialization Account in accordance with Section 5.8, shall not
     exceed one hundred ten percent (110%) of the aggregate amount included for
     such expenses in the then current Commercialization Plan and Budget, unless
     the JSC approves such excess expenses.

8.7  Credit for Payments made by SaSy to ViroPharma. If ViroPharma receives from
     SaSy a royalty pursuant to Section 5.1(a)(iii) of the SaSy Agreement or a
     payment pursuant to Section 5.1(a)(iv) of the SaSy Agreement, within
     fifteen (15) days of ViroPharma's receipt of any such payment, ViroPharma
     shall pay to Aventis ****** percent (******%) of the amount of such
     payments. The Parties shall renegotiate such percentage, but in any case to
     a percentage of at least ****** percent (******%), in a timely fashion and
     in good faith if either:

     8.7.1     SaSy receives Regulatory Approval to market a VP Product for any
               Additional Indication or any Other Indication outside the
               Territory, or

     8.7.2     The actual amounts spent after the Effective Date to obtain
               Regulatory Approval of the First Indication and the Second
               Indication in the Territory exceed ****** U.S. dollars ($******).

     In addition, if Aventis obtains from SaSy exclusive or co-exclusive rights
     to develop, use, sell, offer for sale, have sold, make and have made,
     import and export, any VP Product in Japan, ViroPharma shall no longer be
     obligated to pay

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     Aventis any part of the royalty or other amount received by ViroPharma from
     SaSy pursuant to the SaSy Agreement in respect of Japan.

8.8  Manner of Payments.

     8.8.1     Wire Transfer. All sums due to either Party shall be payable in
               United States dollars by bank wire transfer in immediately
               available funds to such bank account in the Territory as each of
               Aventis and ViroPharma shall designate. Aventis shall notify
               ViroPharma's Chief Financial Officer, and ViroPharma shall notify
               Aventis' Treasurer by facsimile of the date and amount of any
               such wire transfer at least one (1) business day before such
               transfer.

     8.8.2     Taxes and Withholding. All payments under this Agreement will be
               made without any deduction or withholding for or on account of
               any tax unless such deduction or withholding is required by
               applicable Laws. If the paying Party is so required to deduct or
               withhold, such Party will: (a) promptly notify the other Party of
               such requirement, (b) pay to the relevant authorities the full
               amount required to be deducted or withheld promptly upon the
               earlier of determining that such deduction or withholding is
               required or receiving notice that such amount has been assessed
               against the other Party, and (c) promptly forward to the other
               Party an official receipt (or certified copy) or other
               documentation reasonably acceptable to the other Party evidencing
               such payment to such authorities.

8.9  Set-Off. In making payments to the other Party hereunder, neither Party
     shall have the right to set-off or recoup any other payments due to it by
     the other Party except as explicitly provided in Section 8.5.3, and except
     that Aventis shall have the right to set-off for any amounts due to it from
     ViroPharma for:

     8.9.1     obsolete launch stocks required to be repurchased pursuant to
               Section 6.2.4,

     8.9.2     the amount of any payments under Section 10.6.2(b),
               10.6.2(c)(iv), 12.4.3(f), 13.7.3(a) and 13.7.3(b)(vi).

8.10 Interest on Late Payments. If any payment under this Article 8 is late,
     interest shall accrue on the past due amount at a rate equal to the lower
     of the (a) highest lawful interest rate in the Territory, and (b) the prime
     rate effective for the first date on which the payment was delinquent,
     calculated on an actual/360 basis, as quoted in The Wall Street Journal.
                                                     -----------------------

8.11 Financial Records.

     8.11.1    Records. Each Party shall keep and maintain accurate and complete
               records of all figures and transactions known to it that are
               necessary to determine accurately, under U.S. Generally Accepted
               Accounting

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               Principles , the sums due to each Party under this Agreement,
               which shall include, but not be limited to, in the case of
               Aventis, Net Sales, Net Profits (Losses), and Aventis' and
               Aventis' Affiliates' Commercialization Expenses, and in the case
               of ViroPharma, ViroPharma's and ViroPharma's Affiliates'
               Development Expenses and Commercialization Expenses. Each Party
               shall maintain and cause its Affiliates to maintain such records
               for a period of at least three (3) years after the end of the
               Calendar Year in which they were generated.

     8.11.2    Audits. During the Term of this Agreement and three (3) years
               thereafter, upon thirty (30) days prior written notice from a
               Party (the "Auditing Party"), the other Party (the "Audited
               Party") shall permit an independent certified public accounting
               firm of nationally recognized standing selected by the Auditing
               Party and reasonably acceptable to the Audited Party, to examine,
               at the Auditing Party's sole expense, the relevant books and
               records of the Audited Party and its Affiliates as may be
               reasonably necessary to verify the accuracy of the reports
               submitted by the Audited Party in accordance with Section 8.5,
               including without limitation, the accuracy of Development
               Expenses charged to a Party's Development Account,
               Commercialization Expenses and Detail Cost of VP Product charged
               to a Party's Commercialization Account, and the number and type
               of Details performed, the calculation of Net Sales, and the
               calculation and allocation of Net Profits (Losses). An
               examination by a Party under this Section 8.11.2 shall occur not
               more than once in any Calendar Year and shall be limited to the
               pertinent books and records for any Calendar Year ending not more
               than thirty-six (36) months before the date of the request. The
               accounting firm shall be provided access to such books and
               records at the Audited Party's facility(ies) where such books and
               records are normally kept and such examination shall be conducted
               during the Audited Party's normal business hours. The Audited
               Party may require the accounting firm to sign a standard non-
               disclosure agreement before providing the accounting firm access
               to the Audited Party's facilities or records. Upon completion of
               the audit, the accounting firm shall provide each Party with a
               written report disclosing whether the reports submitted by the
               Audited Party are correct or incorrect, whether the calculation
               of Net Sales, the calculation and allocation of Net Profits
               (Losses) is correct or incorrect, and, in each case, the specific
               details concerning any discrepancies.

     8.11.3    Underpayments/Overpayments. If such accounting firm concludes
               that additional payments were due to a Party, the other Party
               shall make such payments, together with any interest that may be
               due thereon as provided in Section 8.10 within thirty (30) days
               of the date such other Party receives such accountant's written
               report so correctly concluding. If such underpayment exceeds five
               percent (5%) of the amount actually paid to the Auditing Party,
               the Audited Party also shall reimburse the Auditing Party for the
               out-of-pocket expenses incurred in conducting the audit,

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                    except in the event that such underpayment was due to any
                    inaccurate information provided by the Auditing Party.

          8.11.4    Confidentiality. All financial information of a Party that
                    is subject to review under this Section 8.11 shall be deemed
                    to be Confidential Information subject to the provisions of
                    Article 11.

9.  CONTRACT PROMOTION OF AVENTIS PRODUCT.

     9.1  Aventis Product Detailing Right and License. Aventis hereby grants
          ViroPharma the royalty free, non-exclusive, non-sublicensable right
          and license under any Patents, trademarks, copyrights, trade secrets
          or other intellectual property covering Aventis Product(s) owned or
          Controlled by Aventis to the extent necessary to perform the
          activities described in this Article 9.

     9.2  Selection of Aventis Product.

          9.2.1     Products Available for Selection. The Aventis Product(s)
                    shall be selected by Aventis in its sole discretion from
                    among the following prescription pharmaceutical products:

                    (a)  ****** (******)******,

                    (b)  the ****** brand of products including, but not limited
                         to:

                         (i)  ****** (****** and ******) ******, and

                         (ii) ****** (******) ******,

                         Aventis may request that ViroPharma distribute Samples
                         for more than a single ****** product for any Details
                         performed for the ****** brand of products, provided
                         that Aventis reimburses ViroPharma for all incremental
                         costs, if any, incurred by ViroPharma as a result of
                         distributing Samples for more than one ****** product,
                         and

                    (c)  any other prescription pharmaceutical product owned or
                         Controlled by Aventis for which the prescriber
                         population to which such product is Detailed
                         substantially overlaps with the prescriber population
                         to which VP Product will be Detailed such that a
                         geographical realignment of ViroPharma's force of sales
                         representatives will not be required for the Detailing
                         of VP Product,

                    in each case to the extent and for so long as Aventis owns
                    or Controls the right to permit ViroPharma to Detail such
                    product. Each product selected under Section 9.2.3, as may
                    be changed from time to time consistent with Section 9.2.3,
                    shall be deemed the "Aventis Product."

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                                                                         Page 75
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          9.2.2     Detailing Right. Beginning on January 1, 2002, and
                    continuing until the termination of ViroPharma's right to
                    promote Aventis Products as set forth in Section 9.5.2,
                    ViroPharma shall Detail Aventis Products using a sales force
                    as set forth in Sections 9.4.1 and 9.4.2.

          9.2.3     Selection and Change. On or before November 30, 2001,
                    Aventis shall notify ViroPharma in writing which two (2)
                    Aventis Products shall be licensed to ViroPharma to promote.
                    At least thirty (30) days before the Launch Date, Aventis
                    shall provide ViroPharma with notice of which Aventis
                    Product ViroPharma shall no longer Detail following the
                    Launch Date. After the Launch Date, but subject to Section
                    9.5, ViroPharma hereby agrees to Detail one (1) Aventis
                    Product. Aventis shall have the right on ninety (90) days'
                    prior written notice to change its selection of Aventis
                    Product(s) from among those listed in Section 9.2.1. In
                    addition, if Aventis should lose ownership or Control of the
                    right to permit ViroPharma to Detail an Aventis Product then
                    currently licensed to ViroPharma, then Aventis shall no
                    later than sixty (60) days after such loss, select a new
                    product from among those listed in Section 9.2.1 that
                    ViroPharma shall be licensed to promote. Until such new
                    product has been made available to ViroPharma for Detailing,
                    Aventis shall continue to pay ViroPharma the applicable
                    Detail Costs for Aventis Products for the maximum number of
                    Details that ViroPharma would have been permitted to perform
                    if Aventis had not lost ownership or Control of the right to
                    permit ViroPharma to Detail such Aventis Product.
                    Notwithstanding the provisions of Section 9.2.1(c), if
                    Aventis should lose ownership or Control of the right to
                    permit ViroPharma to Detail an Aventis Product then
                    currently licensed to ViroPharma, and if Aventis has no
                    product meeting the requirements of Section 9.2.1(c), then
                    ViroPharma agrees to accept as an Aventis Product a primary
                    care product from Aventis' product portfolio.

          9.2.4     Tertiary Sampling or Merchandising. After the Launch Date,
                    at Aventis' election and sole cost for Samples of Aventis
                    Products and promotional materials, the distribution of such
                    Samples and materials, and all incremental costs relating to
                    required Sample accountability activities in addition to
                    those related to other scheduled Details, but with no
                    additional payment required to ViroPharma, during the period
                    that ViroPharma is Detailing Aventis Product(s), Aventis may
                    require ViroPharma to perform a Sample or merchandising drop
                    in association with any already scheduled Details. Such
                    Sample or merchandising drop shall account for no more than
                    five percent (5%) of the total time of such call.

     9.3  Detailing Preparation and Support.

          9.3.1     Training for Aventis Product Detailing. Aventis shall be
                    solely responsible for providing training facilities,
                    trainers and all content to train

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                    ViroPharma's sales representatives on the Aventis
                    Product(s), the relevant disease states, and the procedures
                    for communication and monitoring pursuant to Section
                    9.6.7(a), in preparation for the promotion of the Aventis
                    Product(s). Aventis shall use commercially reasonable
                    efforts to make its corporate lodging rate available to
                    ViroPharma for the lodging of ViroPharma's sales
                    representatives attending training under this Section 9.3.1.
                    Aventis shall permit ViroPharma to send representatives to
                    attend and observe such training. ViroPharma shall pay and
                    be solely responsible for traveling and accommodation
                    expenses incurred by ViroPharma's sales representatives.

          9.3.2     Samples and Promotional Materials. Aventis shall at its own
                    cost provide adequate supplies of promotional materials for
                    use in Detailing directly to each of ViroPharma's sales
                    representatives Detailing Aventis Product. Aventis shall at
                    its own cost provide adequate supplies of Aventis Product
                    Samples for use in Detailing to a central distribution
                    facility designated by ViroPharma. Subject to Sections
                    9.2.1(b) and 9.2.4, ViroPharma shall bear the costs of
                    distributing such Samples to its sales representatives, and
                    all Sample accountability costs for such Samples from the
                    distribution center.

          9.3.3     Promotional Budget. Aventis shall provide ViroPharma's sales
                    representatives with a nominal promotional budget for
                    activities such as "Lunch and Learn" programs for use in
                    support of such sales representatives' Detailing.

     9.4  Aventis Product Detailing.

          9.4.1     Allocation of Calls and Details for Aventis Product(s).

                    (a)  Before the Launch Date. Before the Launch Date, the
                         following will apply to Calls and Details of Aventis
                         Product performed by ViroPharma: During the period in
                         which ViroPharma is Detailing two (2) Aventis Products,
                         without the prior written consent of Aventis,
                         ViroPharma shall not perform more than ****** Primary
                         Details and ****** Secondary Details per month
                         (together, the "Detail Maximum"), pro-rated for any
                         partial month based on the number of days elapsed in a
                         month of 30 days. Aventis shall pay ViroPharma for the
                         Details actually made to Aventis Product Target
                         Prescribers, except as otherwise provided in Section
                         9.2.3, but in any event for no more Details than the
                         Detail Maximum. ViroPharma shall perform Details in the
                         manner and schedule reasonably provided by Aventis,
                         including without limitation, the Aventis Product
                         Target Prescribers and the positions (i.e., Primary or
                         Secondary) in which each Aventis Product will be
                         Detailed. All of the Calls regarding Aventis Products
                         performed by ViroPharma shall be to Aventis Product
                         Target Prescribers. The ViroPharma

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                         sales representatives who are Detailing Aventis Product
                         shall not Detail any product (including any product
                         controlled by an Affiliate or Third Party) other than
                         an Aventis Product.

                    (b)  After the Launch Date. After the Launch Date, the
                         following will apply to Details of Aventis Product
                         performed by ViroPharma: ViroPharma shall have the
                         right to perform up to ****** Secondary Details per
                         month to Detail the single Aventis Product to Aventis
                         Product Target Prescribers; provided, that such Aventis
                         Product Target Prescribers are within the top ******
                         (******) deciles for Aventis Product Target Prescribers
                         as determined by a Third Party pharmaceutical marketing
                         consultant acceptable to both Parties, pursuant to
                         Section 9.2.3. Notwithstanding anything to the contrary
                         in this Article 9, for any month, Aventis shall not be
                         obligated to pay ViroPharma for any Secondary Details
                         of Aventis Product to other than the Aventis Product
                         Target Prescribers, which Details are in excess of
                         ******% of the total number of Secondary Details of
                         Aventis Product performed by ViroPharma in such month.
                         Such Details of Aventis Product shall be recorded as a
                         Secondary Detail using the sales tracking method then
                         in use by ViroPharma consistent with Section 5.7.3.

           9.4.2    Tranche Launch Plan and Compensation to ViroPharma for
                    Details.

                    (a)  First Tranche. ViroPharma will have at least ******
                         (******) sales representatives ready to Detail Aventis
                         Product(s) on January 1, 2002. If on January 1, 2002,
                         ViroPharma does not have at least ****** (******)
                         ViroPharma sales representatives ready to Detail
                         Aventis Product(s), ViroPharma ******, Aventis Product.
                         If, at any time after January 1, 2002, ViroPharma has
                         at least ****** (******) sales representatives ready to
                         Detail Aventis Product, then ****** ViroPharma the
                         ****** for each Detail or call performed by ******
                         (******) ViroPharma sales representatives.

                    (b)  Second Tranche. In addition to the sales
                         representatives described in Section 9.4.2(a),
                         ViroPharma will have at least an additional ******
                         (******) sales representatives ready to Detail Aventis
                         Product(s) on February 1, 2002. If on February 1, 2002,
                         ViroPharma does not have at least ****** (******)
                         ViroPharma sales representatives ready to Detail
                         Aventis Product(s), Aventis ****** Aventis Product
                         performed by ****** (******) ViroPharma sales
                         representatives. Subject to Section 9.5.2(b-c), if, at
                         any time after February 1, 2002, ViroPharma has at
                         least ****** (******) sales representatives ready to
                         Detail Aventis Product, then Aventis ****** ViroPharma
                         the applicable ****** for each

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                                                                         Page 78
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                         Detail or call performed by up to ****** (******)
                         ViroPharma sales representatives.

                    (c)  Representatives. ViroPharma shall, at its sole expense,
                         recruit, interview and hire as its employees all sales
                         representatives required under this Section 9.4.2. The
                         ViroPharma sales representatives shall be suitably
                         educated and trained and shall be professional in
                         manner and appearance. On Aventis' reasonable request,
                         consistent with Laws, ViroPharma shall remove from the
                         Detailing of Aventis Products any sales representative
                         Detailing Aventis Products, provided that such removal
                         can be appropriately justified and documented.

            9.4.3   Reconciliation. ViroPharma shall invoice Aventis, with
                    appropriate detail, for the costs of Details or Calls, as
                    applicable, for Aventis Products, made pursuant to this
                    Article 9, within fifteen (15) days of the end of each
                    month. Aventis shall pay any such invoice within thirty (30)
                    days of receipt.

     9.5    Term of Aventis Product Detailing Right.

            9.5.1   Extension. ViroPharma's right and license under Section 9.1
                    may be renewed by Aventis for successive one (1) year terms
                    by giving ViroPharma, not later than September 1 of any
                    Calendar Year, written notice of Aventis' proposal to renew
                    ViroPharma's right and license for the following Calendar
                    Year. ViroPharma may reject such renewal by providing
                    Aventis with written notice of such rejection within thirty
                    (30) days of receiving Aventis' notice of proposed
                    extension.

            9.5.2   Termination.

                    (a)  ViroPharma's right and license under Section 9.1 shall
                         terminate upon the termination or expiration of this
                         Agreement for any reason.

                    (b)  Aventis shall have the right, but shall not be
                         required, to terminate ViroPharma's right and license
                         under Section 9.1 by providing written notice to
                         ViroPharma if, as of ******, ******. The right to
                         terminate under this Section 9.5.2(b) shall expire upon
                         the first day that ViroPharma has employed ******
                         (******) ******.

                    (c)  Aventis shall have the right to terminate ViroPharma's
                         right and license under Section 9.1 by providing
                         ViroPharma with written notice of termination of such
                         right by ******, which termination shall become
                         effective on ******. If Aventis exercises its right to
                         terminate ViroPharma's promotion of Aventis Product
                         pursuant to this Section 9.5.2(c), then at ViroPharma's
                         option, either:

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                                                                         Page 79
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                         (i)  Aventis shall pay ViroPharma ****** U.S. dollars
                              (U.S. $******) no later than five (5) days after
                              (x) the effective date of such termination, or (y)
                              ******, if the first Regulatory Approval in the
                              United States of an NDA for a VP Product for the
                              First Indication has not been granted before
                              ******, provided that Aventis has not terminated
                              this Agreement prior to ******, which amount shall
                              be fully creditable against the payment to be made
                              under Section 8.1.8(a), except that ViroPharma
                              shall not be permitted to exercise its option to
                              receive, and Aventis shall not be required to pay
                              such amount if Aventis has already paid the
                              milestone set forth in Section 8.1.8(a), or

                         (ii) Aventis shall make no such payment, the rights and
                              licenses granted under Section 9.1 shall
                              terminate, and no amount shall be credited against
                              the payment to be made under Section 8.1.8(a).

     9.6  Scope of Activities with Respect to Aventis Products.

          9.6.1     Field Evaluation. On Aventis' reasonable request and with
                    reasonable advance notice, ViroPharma shall cause its sales
                    force managers to:

                    (a)  accompany sales representatives on calls, and

                    (b)  conduct meaningful field evaluations.

                    At Aventis' request, ViroPharma shall allow Aventis'
                    designated representative to accompany ViroPharma sales
                    representatives on such calls. Aventis reserves the right to
                    conduct field call and/or call report audits.

          9.6.2     Surveys. On a regular basis, and otherwise at Aventis'
                    reasonable request, ViroPharma shall permit Aventis to
                    conduct satisfaction surveys, in a mutually acceptable form,
                    of physicians with whom ViroPharma sales representatives
                    have interacted and promptly share the results with
                    ViroPharma.

          9.6.3     Reports. On or before the twentieth (20th)day of each month,
                    on Aventis' standard and customary forms as provided to
                    ViroPharma , ViroPharma shall provide Aventis with the
                    following periodic reports relating to the previous month:

                    (a)  a monthly executive summary for Aventis Products and
                         market and competitive intelligence,

                    (b)  a monthly turnover report, and

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                    (c)  a periodic listing of territory personnel and days/week
                         filled and unfilled.

          9.6.4     Promotional Material. Aventis shall be solely responsible
                    for determining the content, quantity and method of
                    distribution to Detail recipients of the Aventis Product
                    promotional materials. In connection with the Detailing of
                    the Aventis Product, the ViroPharma sales representatives
                    shall use only the product labeling and promotional
                    materials provided by Aventis.

          9.6.5     Product Claims. ViroPharma shall instruct and require its
                    sales representatives to limit their statements and claims
                    regarding the Aventis Products, including statements and
                    claims concerning safety and efficacy, to those that are
                    consistent with the Aventis Product labeling and the Aventis
                    Product promotional materials. No ViroPharma sales
                    representative may add, delete, or modify claims of efficacy
                    or safety in the Detailing of Aventis Products, nor make any
                    changes in the Aventis Product promotional materials, nor
                    shall any ViroPharma sales representative make any
                    disparaging, untrue or misleading statements about Aventis
                    or any of its products, or take any other action that would
                    jeopardize the goodwill or reputation of the Aventis Product
                    or Aventis.

          9.6.6     Supervision of Personnel. ViroPharma shall be responsible
                    for initiating and implementing all actions regarding
                    hiring, promotion, discipline, discharge, compensation,
                    processing of grievances and monitoring of the professional
                    appearance, demeanor and conduct of its sales
                    representatives.

          9.6.7     Communications; Monitoring.

                    (a)  Communications from Third Parties. ViroPharma and its
                         sales representatives shall forward to Aventis all
                         comments, statements, requests and inquiries from the
                         medical profession or any other Third Party relating to
                         the Aventis Products, which comments, statements,
                         requests and inquiries are:

                         (i)    out of the ordinary,

                         (ii)   not covered by product labeling, or

                         (iii)  safety-related.

                         All responses to the medical profession or other Third
                         Parties shall be handled solely by Aventis.

                    (b)  Adverse Event Reports. ViroPharma shall notify Aventis
                         as soon as practicable of receipt of any Adverse Drug
                         Experience, and in any event, no later than forty-eight
                         (48) hours after ViroPharma

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                         receives notice of a Serious Adverse Drug Experience,
                         and no later than ten (10) days after ViroPharma
                         receives a Non-Serious Adverse Drug Experience.
                         ViroPharma shall submit all Adverse Drug Experience
                         reports on MEDWATCH 3500A forms and transmit such forms
                         via facsimile to Aventis' Drug Product Safety Division
                         at the address an fax number provided to ViroPharma by
                         Aventis in writing.

               (c)       Threatened Agency Action. ViroPharma shall notify
                         Aventis as soon as practicable after ViroPharma learns
                         of any threatened or pending action by any Regulatory
                         Authority which may materially and adversely affect the
                         Aventis Product. ViroPharma shall, at the request and
                         sole expense of Aventis, cooperate with Aventis in
                         formulating a procedure for taking appropriate action.

     9.6.8     Return/Recall.

               (a)       Returned Products. ViroPharma may not authorize the
                         return of any Aventis Product without the prior written
                         approval of Aventis. All Aventis Products returned to
                         ViroPharma shall be shipped to Aventis in accordance
                         with Aventis' returned goods policy, at Aventis' sole
                         cost.

               (b)       Recall. At Aventis' reasonable request and sole cost,
                         ViroPharma shall provide reasonable assistance to
                         Aventis in (i) obtaining and receiving any Aventis
                         Product that has been recalled, and (ii) performing all
                         other field corrections resulting from compliance
                         issues. Aventis shall reimburse all direct documented
                         costs incurred by ViroPharma with respect to
                         participating in any such recall or field corrections.

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10.  INTELLECTUAL PROPERTY.

     10.1  Inventions, Improvements, and Data. Aventis and ViroPharma shall be
           the joint owners of Intellectual Work Product. Each Party shall
           promptly disclose to the other Party all Intellectual Work Product
           and the Parties shall have no claim for additional compensation for
           the Intellectual Work Product. The Parties agree to execute any
           documents or undertake any further actions as may be reasonably
           necessary to effectuate the foregoing.

           10.1.1  Post Agreement Term License in U.S. and Canada. Effective
                   upon expiration or termination of this Agreement, Aventis
                   hereby grants to ViroPharma a perpetual, irrevocable,
                   exclusive, even as to Aventis, royalty-free and
                   sublicenseable license, in and to Aventis' interest in the
                   Intellectual Work Product but only to the extent such
                   Intellectual Work Product covers the use of a pharmaceutical
                   product to prevent or treat picornavirus infections in humans
                   in the U.S. and Canada.

          10.1.2   Licenses to Comply with the SaSy Agreement. The Parties shall
                   take the following steps to assure appropriate licensing of
                   Intellectual Work Product constituting inventions or
                   discoveries relating to VP Compound and/or VP Product
                   considered to be developed by ViroPharma or on behalf of
                   ViroPharma under the SaSy Agreement (the "SaSy IP") to SaSy:

                   (a)  Before beginning any development activities that may
                        result in SaSy IP, on an invention-by-invention and
                        discovery-by-discovery basis, the Parties shall agree on
                        the commercially reasonable market terms as between the
                        Parties for the license to be granted by Aventis to
                        ViroPharma regarding the use of such SaSy IP outside the
                        U.S. and Canada for the term of the SaSy Agreement, as
                        and to the extent necessary for ViroPharma to comply
                        with its obligations to license such SaSy IP to SaSy
                        under the SaSy Agreement (each a "SaSy IP License"), and
                        upon agreement on such commercial terms, the Parties
                        shall enter into such SaSy IP License.

                   (B)  If the Parties could not in a timely manner, or have not
                        agreed, on an invention-by-invention and discovery-by-
                        discovery basis, on the commercial terms of a SaSy IP
                        License as set forth in Section 10.1.2(a) permitting
                        ViroPharma to comply with its licensing obligations with
                        respect to SaSy IP under the SaSy Agreement, then after
                        receipt of notice of the existence of such SaSy IP from
                        ViroPharma, Aventis shall be deemed to have granted a
                        respective SaSy IP License as, and to the extent
                        necessary for ViroPharma to comply with its licensing
                        obligations with respect to SaSy IP under the SaSy
                        Agreement, and the Parties shall in good faith negotiate
                        the commercially reasonable market terms for such SaSy
                        IP License promptly after the making of such license.

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     10.2  VP Patent Rights.

           10.2.1  Prosecution and Maintenance of the SaSy Patents.

                   (a)  SaSy Patents for which SaSy has Primary Responsibility.
                        ViroPharma shall make, or shall use best efforts to
                        ensure that SaSy makes adequate filings for, and
                        prosecutes and maintains, all SaSy Patents and related
                        applications in the Territory that are material to the
                        matters contemplated in this Agreement, and for which
                        SaSy has the first right to prosecute and maintain such
                        patents in the Territory under the SaSy Agreement.
                        ViroPharma shall use best efforts to ensure that SaSy
                        files applications and takes any other actions necessary
                        to obtain patent extensions and supplementary protection
                        certificates, where available in the Territory, for SaSy
                        Patents in the Territory that are material to the
                        matters contemplated in this Agreement, and for which
                        SaSy has the first right to obtain patent extensions and
                        supplementary protection certificates for such patents
                        in the Territory under the SaSy Agreement.

                   (b)  SaSy Patents for which ViroPharma has Primary
                        Responsibility. ViroPharma shall prosecute and maintain
                        all SaSy Patents and related pending applications in the
                        Territory that are material to the matters contemplated
                        in this Agreement, and for which ViroPharma has the
                        first right to prosecute and maintain such patents in
                        the Territory under the SaSy Agreement. ViroPharma shall
                        file all applications and take any other actions
                        necessary to obtain patent extensions and supplementary
                        protection certificates for SaSy Patents where available
                        in the Territory for SaSy Patents in the Territory that
                        are material to the matters contemplated in this
                        Agreement, and for which ViroPharma has the first right
                        to obtain patent extensions and supplementary protection
                        certificates for such patents in the Territory under the
                        SaSy Agreement.

                   (c)  Notifications. ViroPharma shall consult with Aventis
                        upon ViroPharma's receipt of notice from SaSy that SaSy
                        contemplates abandoning any SaSy Patents or related
                        applications that are material to the matters
                        contemplated in this Agreement. ViroPharma shall consult
                        with Aventis before making any decision to abandon any
                        SaSy Patents or related applications that are material
                        to the matters contemplated in this Agreement, to the
                        extent that ViroPharma has such right. At Aventis'
                        reasonable request ViroPharma shall advise Aventis of
                        the status of pending applications, shall provide
                        Aventis with copies of documentation concerning such
                        applications, to the extent that ViroPharma has such
                        right. ViroPharma shall consult with Aventis before

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                        ViroPharma or SaSy, as applicable, and with respect to
                        SaSy, as feasible and permitted, takes any action
                        materially affecting the scope of patent coverage
                        relating to any VP Compound or VP Product.

           10.2.2  Prosecution and Maintenance of the ViroPharma Patents.
                   ViroPharma shall make adequate filings for and prosecute and
                   maintain all ViroPharma Patents and related applications in
                   the Territory, if any, unless ViroPharma and Aventis mutually
                   determine that any such ViroPharma Patent or related
                   application is not material to the matters contemplated in
                   this Agreement. ViroPharma and Aventis shall mutually agree
                   before ViroPharma abandons any ViroPharma Patents or related
                   applications that relate to the matters contemplated in this
                   Agreement. At Aventis' reasonable request, ViroPharma shall
                   advise Aventis of the status of pending applications, shall
                   provide Aventis with copies of documentation concerning such
                   applications and ViroPharma and Aventis shall mutually agree
                   before ViroPharma takes any action materially affecting the
                   scope of patent coverage relating to any VP Compound or VP
                   Product. ViroPharma shall file all applications and take any
                   other actions necessary to obtain patent extensions and
                   supplementary protection certificates for ViroPharma Patents
                   where available in the Territory unless ViroPharma and
                   Aventis mutually determine that any such ViroPharma Patent or
                   application is not material to the matters contemplated by
                   this Agreement.

           10.2.3  IWP Patents. ViroPharma shall have the first right and
                   option, and to the extent that ViroPharma does not make use
                   of such option, the Aventis shall be permitted to make, on
                   behalf of both Parties, adequate filings for, and to
                   prosecute, maintain and obtain any extensions or
                   supplementary protection certificates for all IWP Patents and
                   related applications. The Parties shall agree on the content
                   of any IWP Patents to be filed, and on any other action
                   materially affecting the scope of patent coverage relating to
                   any IWP Patent. The prosecuting Party shall advise the other
                   Party of the status of pending applications for IWP Patents
                   and shall promptly provide Aventis with copies of all
                   documentation concerning such applications. The JSC shall
                   determine whether to abandon any IWP Patents. The Parties
                   shall share equally all the costs, other than internal costs,
                   incurred under this Section 10.2.3.

           10.2.4  Enforcement. If either Party becomes aware of any
                   infringement in the Territory of any issued Patent among the
                   SaSy Patents, the ViroPharma Patents, or the IWP Patents, it
                   shall promptly notify the other Party in writing.

                   (a)  SaSy Patents. With respect to any SaSy Patent,
                        ViroPharma shall use commercially reasonable efforts to
                        ensure that SaSy takes, appropriate action to obtain a
                        discontinuance of such infringement, or to bring suit
                        against the Third Party infringer. If SaSy elects

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                                                                         Page 85
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                        pursuant to the SaSy Agreement to permit ViroPharma to
                        undertake appropriate action to obtain a discontinuance
                        of such infringement, then the JSC shall determine what
                        actions to undertake, and ViroPharma shall use
                        commercially reasonable efforts to obtain a
                        discontinuance of such infringement by performing such
                        actions. The Parties shall share equally the costs of
                        any such activities and any amounts received from Third
                        Parties as a result of such activities.

                   (b)  ViroPharma Patents. With respect to any ViroPharma
                        Patent, the JSC shall consider whether to take any
                        action to obtain a discontinuance of such infringement,
                        and whether to bring suit against the Third Party
                        infringer. The JSC may designate either Party to take
                        any action against the Third Party infringer, which
                        Party shall use commercially reasonable efforts to
                        obtain a discontinuance of such infringement by taking
                        such action. If the JSC designates Aventis to take such
                        action then ViroPharma shall ensure that Aventis
                        receives the rights, other than ownership rights in the
                        underlying intellectual property, necessary to take the
                        aforementioned action. The Parties shall share equally
                        the costs of any activities under this Section 10.2.4(b)
                        and any amounts received from Third Parties as a result
                        of such activities.

                   (c)  IWP Patents. With respect to any IWP Patent in the Field
                        and in the Territory, the JSC shall determine the
                        appropriate action to obtain a discontinuance of such
                        infringement, and may designate either Party to bring
                        suit against the Third Party infringer. The Parties
                        shall consult before taking any such appropriate action
                        to obtain a discontinuance of such infringement, and
                        before bringing suit against the Third Party infringer.
                        The Parties shall share equally the costs of any
                        activities under this Section 10.2.4(c) and any amounts
                        received from Third Parties as a result of such
                        activities, except that if either Party in its
                        reasonable discretion, determines not to take any action
                        to obtain a discontinuance of such infringement, or to
                        bring suit against the Third Party infringer, the other
                        Party's sole remedy shall be to take such action at its
                        own cost and risk and any financial benefit resulting
                        from such action shall be such other Party's alone. The
                        first Party then shall ensure that the other Party
                        receives the rights necessary to take the aforementioned
                        action. The first Party shall reasonably assist the
                        other Party in taking such action at the other Party's
                        expense.

           10.2.5  Alleged Infringement of Third Party Patents.

                   (a)  Notice. If the making, having made, importing,
                        exporting, using, distributing, marketing, promoting,
                        offering for sale or selling any

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                                                                         Page 86
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                        VP Compound and/or VP Product, under this Agreement, is
                        alleged by a Third Party to infringe such Third Party's
                        patent, the Party becoming aware of such allegation
                        shall promptly notify the other Party. Additionally, if
                        either Party determines that, based upon the review of a
                        Third Party's patent or patent application, it may be
                        desirable to obtain a license from such Third Party with
                        respect thereto so as to avoid any potential suit
                        between either Party and such Third Party, such Party
                        shall promptly notify the other Party of such
                        determination, subject to the Parties' entering into a
                        joint privilege agreement.

                   (b)  Negotiation and Litigation. Subject to any limitations
                        or rights contained in the SaSy Agreement, ViroPharma
                        shall have the right to negotiate with said Third Party
                        for a suitable license or assignment. If a Third Party
                        sues either of the Parties asserting that the Parties'
                        promotion and sales of VP Product under this Agreement
                        infringes or will infringe such Third Party's Patents in
                        the Field, ViroPharma shall control the defense of such
                        action and any discussions relating to the settlement or
                        compromise of such action. ViroPharma shall not enter
                        into any settlement that would adversely affect Aventis'
                        rights under this Agreement without the prior written
                        consent of Aventis.

                   (c)  Coverage of Costs. Any royalties or other amounts
                        required to be paid to a Third Party to obtain a
                        suitable license pursuant to Section 10.2.5(b) above to
                        use, sell, offer for sale, make, have made, import or
                        export, (i) any VP Compound or (ii) the VP Product
                        formulation for which NDA 21-245 was submitted to the
                        FDA on July 31, 2001, shall be at the sole cost and
                        responsibility of ViroPharma and shall not be deemed a
                        Commercialization Expense (except to the extent that the
                        SaSy Royalties are reduced to the same extent by any
                        such payment, in which case, any such payment shall be
                        deemed a SaSy Royalty.) Notwithstanding anything to the
                        contrary herein, the Parties shall share equally any
                        responsibility for any Third Party patent infringement
                        action concerning a Combination Product to the extent
                        that the claim of infringement alleges use of the VP
                        Compound in connection with any other Compound or
                        product.

     10.3  Trademarks and Logos.

           10.3.1  Trademark Selection, Ownership and Use. VP Product shall be
                   promoted and sold under Trademarks selected by ViroPharma and
                   SaSy in their sole discretion. If VP Product is not promoted
                   and sold under the trademark PICOVIR, ViroPharma shall obtain
                   Aventis' agreement before proposing to SaSy any of the other
                   Trademarks, or before selecting any new trademark, to be used
                   in promoting and selling VP Product. The

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                                                                         Page 87
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                   Parties understand that SaSy is the sole owner of the
                   Trademarks and any goodwill pertaining therein. Aventis shall
                   use the Trademarks only to the extent explicitly permitted by
                   this Agreement and only in the manner provided in this
                   Agreement, including without limitation Section 5.16. Upon
                   the termination of Aventis' right to promote VP Product,
                   including without limitation, the termination of this
                   Agreement for any reason, Aventis shall immediately stop
                   using the Trademarks in any way.

           10.3.2  Trademark Prosecution and Maintenance. ViroPharma shall use
                   reasonable efforts to ensure that the trademark PICOVIR may
                   be used for the promoting and selling of VP Product.
                   Consistent with Laws, ViroPharma shall make, or shall use
                   reasonable efforts to ensure that SaSy makes, adequate
                   filings for, and prosecute and maintain, all Trademarks in
                   the Territory unless ViroPharma reasonably believes that any
                   such Trademark is not material to the matters contemplated in
                   this Agreement. ViroPharma shall consult with Aventis before
                   abandoning, or upon ViroPharma's receipt of notice from SaSy
                   that SaSy contemplates abandoning, any Trademarks that are
                   material to the matters contemplated in this Agreement. At
                   Aventis' reasonable request ViroPharma shall advise Aventis
                   of the status of pending applications, shall provide Aventis
                   with copies of documentation concerning such applications and
                   shall consult with Aventis before taking any action
                   materially affecting the Trademarks that are used for
                   promoting VP Product. The provisions of this Section 10.3.2
                   shall be subject to any limitations or rights contained in
                   the SaSy Agreement.

           10.3.3  Aventis Logo and ViroPharma Logo. Each Party hereby grants to
                   the other Party the right to use, and the other Party hereby
                   agrees to use to the extent requested by the first Party and
                   as agreed to by the JSC, the first Party's Logo on labeling,
                   package inserts and packaging materials for VP Product, all
                   Promotional Materials, Samples and any other materials used
                   in connection with the performance of this Agreement during
                   the Term of this Agreement and until the exhaustion of any
                   such materials existing on the expiration or termination of
                   this Agreement; provided, however, such use shall be
                   consistent with the uses approved by the first Party's
                   representatives on the Joint Steering Committee, or the
                   Marketing Subcommittee thereof, such approval not to be
                   unreasonably withheld and in accordance with such first
                   Party's guidelines for the use of such Logo. Neither Party
                   shall have any rights under this Agreement in or to the other
                   Party's Logo or the goodwill pertaining thereto except as
                   specifically provided for herein.

           10.3.4  Notice of Infringement. If either Party becomes aware of any
                   infringement in the Territory of any Trademark, it shall
                   promptly notify the other Party in writing.

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           10.3.5  Aventis shall not register or attempt to register in the
                   Territory any trade name, trademark, service mark,
                   certification mark, or logo that is confusingly similar to,
                   or that contains elements that are confusingly similar to,
                   any of the Trademarks. ViroPharma shall not register or
                   attempt to register in the Territory any trade name,
                   trademark, service mark, certification mark, or logo that is
                   confusingly similar to, or that contains elements that are
                   confusingly similar to or any trademark covering an Aventis
                   Product.

     10.4  Promotional Material Copyrights. ViroPharma and Aventis shall jointly
           own all right, title and interest in and to any Promotional Materials
           that are directed to any VP Product, whether generated by Aventis or
           its Affiliates, ViroPharma or its Affiliates, or any Third Parties,
           or by any of the Parties and/or their Affiliates and/or such Third
           Parties jointly, including all applicable copyrights. Aventis and
           ViroPharma shall retain all rights, including, without limitation,
           copyrights and trademarks, to all of their respective existing
           programs and materials in all formats (print, video, audio, digital,
           computer, etc.) regarding sales training, patient education and
           disease management programs currently owned by each, as well as any
           modifications of such programs each may develop in the future which
           are not specific to any VP Product. Aventis and ViroPharma shall,
           from time to time, each notify the other as to the identity of such
           proprietary programs. Each Party grants the other the royalty-free,
           sublicensable right and license in the Territory to use in any
           labeling, package inserts and packaging materials for VP Product, all
           Promotional Materials, Samples and any other materials used in
           connection with the performance of this Agreement any program or
           material that has been specifically adapted for, or directed to, any
           VP Product, during the Term of this Agreement and until the earlier
           of the first anniversary of the termination or expiration of this
           Agreement, and the exhaustion of any such materials existing on the
           expiration or termination of this Agreement.

     10.5  SaSy Agreement. Under no circumstances shall ViroPharma terminate the
           SaSy Agreement without the prior written consent of Aventis.
           ViroPharma shall promptly provide Aventis with: (a) a description of
           any oral conversations with SaSy that materially affect either the
           SaSy Agreement or this Agreement (b) copies of all correspondence
           either delivered by or received by ViroPharma, to or from SaSy, which
           relate to or affect either the SaSy Agreement or this Agreement
           (including, without limitation, any notification, whether orally or
           in writing, concerning the termination of the SaSy Agreement), and
           (c) any written materials and other information prepared in
           connection with any meeting with SaSy prior to any such meeting
           (collectively, "SaSy Information"); but in each case excluding any
           information which ViroPharma is not entitled to disclose to Aventis.
           To the extent that ViroPharma does not have the right to disclose to
           Aventis any SaSy Information and to the extent such SaSy Information
           materially adversely effects Aventis' right pursuant to this
           Agreement, ViroPharma shall use commercially reasonable efforts to
           obtain the right to disclose such SaSy Information to Aventis.

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                                                                         Page 89
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     10.6  Mutual Covenant Upon SaSy Breach.

           10.6.1  SaSy Breach. In the event of any breach or threatened breach
                   of the SaSy Agreement by SaSy:

                   (a)  The Parties shall promptly consult with each other as to
                        the appropriate course of action.

                   (b)  If the Parties mutually agree to give or initiate any
                        notices, actions, challenges, proceedings or
                        negotiations to, against or with SaSy with respect to
                        such breach or alleged breach of the SaSy Agreement (a
                        "SaSy Breach Dispute"):

                        (i)   The Parties will jointly control such SaSy Breach
                              Dispute;

                        (ii)  Each Party shall cooperate fully with the other
                              and act in a reasonable manner and in the best
                              interests of the collaboration formed hereunder
                              with respect to all matters regarding such SaSy
                              Breach Dispute, including, without limitation,
                              bringing together any suits that may be brought
                              against SaSy;

                        (iii) Before contacting SaSy or making any response to
                              SaSy with respect to such SaSy Breach Dispute, a
                              Party shall consult with the other Party and
                              neither Party shall undertake any discussion with
                              SaSy without the participation of the other Party;

                        (iv)  Each Party shall have the right to participate in
                              all discussions with SaSy regarding such SaSy
                              Breach Dispute;

                        (v)   Each Party shall bear its own expenses with
                              respect to such SaSy Breach Dispute; and

                        (vi)  Any economic benefit received by the Parties in
                              connection with any SaSy Breach Dispute shall be
                              shared equally by the Parties, after reimbursement
                              of each Party's reasonable out-of-pocket expenses
                              incurred in connection with such SaSy Breach
                              Dispute.

                   (c)  Neither Party shall enter into any settlement agreement
                        with SaSy without the prior written consent of the other
                        Party which consent shall not be unreasonably withheld
                        or delayed.

           10.6.2  Non-Aventis Breach. If ViroPharma receives notice from SaSy
                   with respect to ViroPharma's breach or alleged breach of the
                   SaSy Agreement

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                                                                         Page 90
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                   and ViroPharma acknowledges that if such breach in fact
                   occurred as alleged by SaSy, then such breach was caused
                   solely by ViroPharma:

                   (a)  ViroPharma Cure. ViroPharma shall promptly take all
                        appropriate actions to cure such breach or alleged
                        breach and shall keep Aventis informed of all such
                        actions taken.

                   (b)  Aventis Option to Cure. In its sole discretion and at
                        any time upon notice to ViroPharma, Aventis shall have
                        the right (but not the obligation), to the extent
                        possible, to cure any and all breaches by ViroPharma of
                        the SaSy Agreement. In furtherance of the foregoing, to
                        the broadest extent permitted under the SaSy Agreement
                        without requiring the prior written consent of SaSy,
                        ViroPharma hereby grants to Aventis any and all rights
                        and non-exclusive licenses necessary in order for
                        Aventis to cure such breach. Aventis shall charge the
                        actual amounts reasonably incurred by it in curing such
                        breach to its Development Account or Commercialization
                        Account (the "Cure Amount"), as appropriate, and in
                        addition ViroPharma shall pay Aventis an amount equal to
                        the Cure Amount, which shall not be charged to either
                        Party's Development Account or Commercialization
                        Account.

                   (c)  Aventis Control of Actions. Aventis shall have the right
                        (but not the obligation), exercisable within thirty (30)
                        days (fifteen (15) days in the event of litigation) of
                        the notice described above in this Section 10.6.2, to
                        initiate, control, or participate in any notices,
                        actions, challenges, proceedings or negotiations to,
                        against or with SaSy with respect to any breach or
                        alleged breach of the SaSy Agreement subject to this
                        Section 10.6.2 (a "Section 10.6.2 Breach Challenge"), as
                        follows:

                        (i)  If Aventis elects to initiate or control any such
                             Section 10.6.2 Breach Challenge, ViroPharma shall,
                             at its sole cost and expense, cooperate fully with
                             Aventis and its counsel, join in any such suits
                             that Aventis brings, and make itself available at
                             Aventis' reasonable request to assist in any such
                             Section 10.6.2 Breach Challenge. Before contacting
                             or making any material response to SaSy with
                             respect to the substance or settlement of such
                             Section 10.6.2 Breach Challenge, Aventis shall
                             consult with ViroPharma and ViroPharma shall have
                             the right to participate in, and Aventis shall not
                             engage in without ViroPharma, any material
                             discussions with SaSy regarding the substance or
                             settlement of such Section 10.6.2 Breach Challenge.

                        (ii) If Aventis fails to elect within the time frame
                             described above in this Section 10.6.2(c), or
                             elects not to initiate or
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                                                                         Page 91
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                               control any such Section 10.6.2 Breach Challenge,
                               Aventis shall, at ViroPharma's sole cost and
                               expense, cooperate fully with ViroPharma and its
                               counsel, join in any such suits that ViroPharma
                               brings, and make itself available at ViroPharma's
                               reasonable request to assist in any such Section
                               10.6.2 Breach Challenge. Before contacting or
                               making any response to SaSy with respect to such
                               Section 10.6.2 Breach Challenge, ViroPharma shall
                               consult with Aventis and Aventis shall have the
                               right to participate in, and ViroPharma shall not
                               engage in without Aventis, any material
                               discussions with SaSy regarding substance or
                               settlement of such Section 10.6.2 Breach
                               Challenge. At any time, upon notice to
                               ViroPharma, Aventis may assume control of such
                               Section 10.6.2 Breach Challenge.

                        (iii)  Each Party shall perform all activities with
                               respect to any Section 10.6.2 Breach Challenge in
                               a reasonable manner, and in the best interests of
                               the collaboration formed hereunder, and shall
                               adopt all reasonable suggestions and
                               recommendations of the other Party with respect
                               to such Section 10.6.2 Breach Challenge. Neither
                               Party shall enter into any settlement agreement
                               with SaSy without the other Party's prior written
                               consent, which consent shall not be unreasonably
                               withheld or delayed.

                        (iv)   Whether or not Aventis assumes control of any
                               Section 10.6.2 Breach Challenge, ViroPharma
                               shall:

                               a.  Reimburse Aventis for all reasonable out-of-
                                   pocket costs and expenses incurred by Aventis
                                   in connection with such Section 10.6.2 Breach
                                   Challenge.

                               b.  Assume and bear full responsibly for or
                                   otherwise reimburse Aventis for any amounts
                                   required to be paid to SaSy or any Third
                                   Party on behalf of SaSy in settlement of the
                                   Section 10.6.2 Breach Challenge, including,
                                   without limitation, any royalties or other
                                   payments, and any such amounts shall not be
                                   treated as a Commercialization Expense or
                                   Development Expense hereunder.

                   (d)  If:

                        (i)    The breach or alleged breach of the SaSy
                               Agreement subject to this Section 10.6.2 is
                               cured,

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                                                                         Page 92
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                        (ii)  The Parties obtain a final non-appealable judgment
                              terminating the Section 10.6.2 Breach Challenge,

                        (iii) There is a judgment regarding the Section 10.6.2
                              Breach Challenge that SaSy and the Parties agree
                              not to appeal; or

                        (iv)  The Parties enter into a binding agreement
                              settling the Section 10.6.2 Breach Challenge,

                        in which case, or as a result of which the SaSy
                        Agreement continues to be in full force and effect, then
                        the provision of this Section 10.6.2 (other than payment
                        obligations or liabilities incurred prior to such time)
                        shall cease to be in effect until the next occurrence of
                        an event triggering the provisions of this Section
                        10.6.2.

           10.6.3  Other Breach. If ViroPharma receives notice from SaSy with
                   respect to ViroPharma's breach or alleged breach of the SaSy
                   Agreement, other than a breach subject to Section 10.6.2:

                   (a)   The Parties shall consult with each other promptly as
                         to the appropriate course of action.

                   (b)   If the Parties agree to give or initiate any notices,
                         actions, challenges, proceedings or negotiations to,
                         against or with SaSy with respect to such breach or
                         alleged breach of the SaSy Agreement (a "SaSy
                         Dispute"):

                         (i)   The Parties will jointly control such SaSy
                               Dispute.

                         (ii)  Each Party shall cooperate fully with the other
                               and perform all activities with respect to such
                               SaSy Dispute in a reasonable manner, and in the
                               best interests of the collaboration formed
                               hereunder, including, without limitation, joining
                               in any suits which may be brought against SaSy,
                               and shall adopt all reasonable suggestions and
                               recommendations of the other Party with respect
                               to such SaSy Dispute.

                   (c)   Each Party shall bear its own expenses with respect to
                         such SaSy Dispute.

                   (d)   Each Party shall have the right to participate in, and
                         neither Party shall undertake, without the other Party,
                         any discussions with SaSy regarding such SaSy Dispute.

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                                                                         Page 93
<PAGE>

               (e)  Neither Party shall enter into any settlement agreement with
                    SaSy without the prior written consent of the other Party
                    which consent shall not be unreasonably withheld or delayed.

11.  CONFIDENTIALITY.

     11.1  Confidential Information.

           11.1.1  General Prohibition on Disclosure and Use. Except to the
                   extent expressly authorized by this Agreement, or otherwise
                   agreed in writing, during the longer of (a) the term of this
                   Agreement and for five (5) years thereafter, (b) the term of
                   the SaSy Agreement and for five (5) years thereafter, (c)
                   perpetually for trade secrets, and (d) until the issuance of
                   a relevant patent for material in a patent application, each
                   Party shall, and shall cause its Affiliates to, maintain in
                   confidence with at least the same degree of care it uses for
                   its own confidential information, but no less than reasonable
                   care, and shall use all Confidential Information disclosed by
                   the other Party only for purposes of this Agreement.

           11.1.2  Permitted Disclosure and Use for Purposes of Agreement.
                   Notwithstanding the foregoing Section 11.1.1, a Party may
                   disclose the other Party's Confidential Information to those
                   of its Affiliates, directors, officers, employees, agents,
                   consultants and sublicensees that have a need to know such
                   Confidential Information in order to achieve the purposes of
                   this Agreement, provided that such Party obtains prior
                   assurances of confidential treatment from such disclosees at
                   least as restrictive as those set forth herein. Each Party
                   will promptly notify the other upon discovery of any
                   unauthorized use or disclosure of the other Party's
                   Confidential Information. Any breach of this obligation of
                   confidentiality by an Affiliate, director, officer, employee,
                   agent, consultant, or sublicensee of a Party shall be deemed
                   a breach by that Party.

           11.1.3  Other Permitted Disclosure and Use. Notwithstanding Section
                   11.1.1, a Party may disclose Confidential Information
                   belonging to the other Party only to the extent such
                   disclosure is reasonably necessary to:

                   (a)  obtain Regulat ory Approval of VP Product;

                   (b)  enforce the provisions of this Agreement;

                   (c)  comply with Laws; or

                   (d)  comply with the requirements of the SaSy Agreement.

                   If a Party deems it necessary to disclose Confidential
                   Information of the other Party pursuant to this Section
                   11.1.3, such Party shall give reasonable advance notice of
                   such disclosure to the other Party to permit

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                                                                         Page 94
<PAGE>

                   such other Party sufficient opportunity to object to such
                   disclosure or to take measures to ensure confidential
                   treatment of such information.

           11.1.4  Disclosure of this Agreement. ViroPharma shall provide SaSy
                   with a copy of this Agreement upon its execution, and such
                   action shall not be a breach of this Agreement.

     11.2  Publications. Each Party shall submit to the other Party for review
           and approval all proposed academic, scientific and medical
           publications and public presentations relating to the VP Compounds,
           VP Product, or any research or development activities under this
           Agreement for review in connection with preservation of Patent
           rights, and trade secrets and/or to determine whether Confidential
           Information should be modified or deleted from the proposed
           publication or public presentation. Written copies of such proposed
           publications and presentations shall be submitted to the
           nonpublishing Party no later than sixty (60) days before submission
           for publication or presentation and the non-publishing Party shall
           provide its comments with respect to such publications and
           presentations within ten (10) business days of its receipt of such
           written copy. The review period may be extended for an additional
           thirty (30) days if the nonpublishing Party can demonstrate a
           reasonable need for such extension including, but not limited to, the
           preparation and filing of patent applications. By mutual agreement,
           this period may be further extended. The Parties will each comply
           with standard academic practice regarding authorship of scientific
           publications and recognition of contribution of other parties in any
           publications relating to the VP Compounds, VP Product, or any
           research or development activities under this Agreement.
           Notwithstanding anything to the contrary in this Section 11.2, this
           Section 11.2 shall apply to material intended to be disclosed at the
           Interscience Conference on Antimicrobial Agents and Chemotherapy
           ("ICAAC"), September 22-25, 2001, and the Annual Meeting of the
           Infectious Diseases Society of America, October 25-28, 2001, only to
           the extent feasible.

     11.3  Public Announcements.

           11.3.1  Except as may be expressly permitted under Section 11.2 or
                   required by applicable Laws, neither Party will make any
                   public announcement of any information regarding this
                   Agreement, the VP Compounds, VP Product, or any research or
                   development activities under this Agreement without the prior
                   written approval of the other Party. Once any written
                   statement is approved for disclosure by the Parties or
                   information is otherwise made public in accordance with the
                   preceding sentence, either Party may make a subsequent public
                   disclosure of the contents of such statement without further
                   approval of the other Party.

           11.3.2  Aventis acknowledges that ViroPharma will file this Agreement
                   with the SEC, and agrees that such filing shall not be a
                   breach of this Agreement provided that the Agreement as filed
                   shall be redacted such that the extent of disclosure shall be
                   limited to that which is legally required to be

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                                                                         Page 95

<PAGE>

                   disclosed, while not adversely affecting the promptness with
                   which ViroPharma can obtain the SEC's clearance of such
                   redaction. ViroPharma will provide Aventis with a copy of any
                   redaction proposed to be submitted with the SEC within a
                   reasonable time prior to submission to the SEC and will adopt
                   reasonable suggestions made by Aventis to the extent
                   consistent with this Section 11.3.2.

12.  CHANGE OF CONTROL.

     12.1  Notice of Change of Control Transactions. Subject to applicable Law,
           ViroPharma shall promptly notify Aventis in the event that ViroPharma
           (a) has entered into an agreement for a Change of Control or (b)
           learns of the initiation of any transaction of the type described in
           Section 12.2.2.

     12.2  Termination of Standstill Agreement. The Standstill Agreement shall
           terminate and be of no further force and effect and Aventis shall
           have the right to acquire any securities of ViroPharma in the event
           that:

           12.2.1  ViroPharma has entered into an agreement for a Change of
                   Control; or

           12.2.2  a tender or exchange offer is made by any Person, other than
                   Aventis or any of its Affiliates, or 13D Group, of which none
                   of Aventis or any of its Affiliates is a party, to acquire
                   Voting Securities of ViroPharma which, if added to the Voting
                   Securities of ViroPharma (if any) already owned by such
                   Person or 13D Group, would result, if consummated in
                   accordance with its terms, in the Beneficial Ownership by
                   such Person or 13D Group of more than fifty percent (50%) of
                   the Total Voting Power of all Voting Securities of ViroPharma
                   then outstanding.

     12.3  Maintenance of SaSy Agreement. Before ViroPharma consummates a Change
           of Control or, to the extent practicable, before it recommends to its
           stockholders a tender or exchange offer of the type described in
           Section 12.2.2, in either case, ViroPharma shall use commercially
           reasonable efforts to ensure that the SaSy Agreement shall continue
           and that the scope and term of Aventis' rights hereunder shall remain
           unaffected and continue on identical economic terms.

     12.4  SaSy Notice of Termination. If any of the events set forth in
           Sections 12.2.1 or 12.2.2, or a Change of Control occurs, and SaSy
           has threatened to terminate or has given written notice of its
           termination of the SaSy Agreement pursuant to Section 12.4(a) of the
           SaSy Agreement, then ViroPharma shall notify Aventis thereof and:

           12.4.1  The Parties shall consult with each other promptly as to the
                   appropriate course of action.

           12.4.2  The Parties shall promptly give and initiate any notices,
                   actions, challenges, proceedings or negotiations to, against
                   or with SaSy to oppose

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                                                                         Page 96

<PAGE>

                   such actual or threatened termination of the SaSy Agreement
                   (a "Termination Challenge"):

                   (a)  The Parties will jointly control such Termination
                        Challenge.

                   (b)  Each Party shall cooperate fully with the other and
                        perform all activities with respect to such Termination
                        Challenge in a reasonable manner, and in the best
                        interests of the collaboration formed hereunder,
                        including, without limitation, joining in any suits
                        which may be brought against SaSy or ViroPharma, and
                        shall adopt all reasonable suggestions and
                        recommendations of the other Party with respect to such
                        Termination Challenge.

                   (c)  Each Party shall bear its own expenses with respect to
                        such Termination Challenge.

                   (d)  Each Party shall have the right to participate in, and
                        neither Party shall undertake, without the other Party,
                        any discussions with SaSy regarding such Termination
                        Challenge.

                   (e)  Neither Party shall enter into any settlement agreement
                        with SaSy without the prior written consent of the other
                        Party which consent shall not be unreasonably withheld
                        or delayed, provided, however, that:

                        (i)  If ViroPharma unreasonably withholds or delays its
                             consent to any settlement agreement that Aventis
                             wishes to accept:

                             a.  Notwithstanding Section 12.4.2(c), ViroPharma
                                 shall reimburse Aventis for all of Aventis'
                                 costs and expenses (including reasonable
                                 attorneys fees) with respect to such
                                 Termination Challenge incurred from the date
                                 that ViroPharma unreasonably withholds or
                                 delays such consent and, thereafter, ViroPharma
                                 shall be responsible for all such costs and
                                 expenses; and

                             b.  If, (x) the Parties obtain a final non-
                                 appealable judgment regarding the Termination
                                 Challenge; (y) there is a judgment in favor of
                                 SaSy which the Parties mutually agree not
                                 appeal or (z) the Parties enter into a binding
                                 agreement settling the Termination Challenge,
                                 which in any case results in the SaSy Agreement
                                 being terminated, ViroPharma shall reimburse
                                 Aventis for its investment in the transactions
                                 contemplated by this Agreement (other than the
                                 transaction contemplated by the Stock Purchase
                                 Agreement) (the "Investment") plus a

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                                                                         Page 97

<PAGE>

                                 ****** percent (******%) return on investment
                                 compounded annually, less all ******
                                 distributed to or retained by Aventis or its
                                 Affiliates pursuant to this Agreement
                                 (together, the "Reimbursement Payment"). The
                                 Investment shall be measured on the basis of
                                 payments made by Aventis pursuant to Sections
                                 8.1 and 8.3, and Aventis' share of Development
                                 Expenses and Commercialization Expenses
                                 incurred through the date of termination of the
                                 SaSy Agreement. The Reimbursement Payment shall
                                 be made within thirty (30) days of the
                                 effective date of the termination of the SaSy
                                 Agreement.

                        (ii)  Aventis shall be deemed to have consented to such
                              settlement agreement if:

                              a.  Aventis' rights under this Agreement are not
                                  materially adversely affected by such
                                  settlement agreement;

                              b.  The economic impact of the proposed settlement
                                  agreement can be determined with reasonable
                                  certainty, such that ViroPharma's obligation
                                  under Section 12.4.2(e)(iii) can be
                                  implemented without dispute.

                        (iii) ViroPharma shall assume and bear full responsibly
                              for or otherwise reimburse Aventis for any amounts
                              required to be paid to SaSy under the settlement
                              agreement, including, without limitation, any
                              royalties or other payments, and any such amounts
                              shall not be treated as a Development Expense or a
                              Commercialization Expense hereunder.

          12.4.3  Temporary Expansion of Aventis Rights. Upon the earlier of (x)
                  the receipt from SaSy of written notice of SaSy's termination
                  of the SaSy Agreement pursuant to Section 12.4(a) of the SaSy
                  Agreement, or (y) the threat from SaSy of an intent to
                  terminate the SaSy Agreement pursuant to Section 12.4(a) of
                  the SaSy Agreement that ViroPharma agrees should effect an
                  expansion of Aventis' rights under this Section 12.4.3, then
                  Aventis shall have the right (but not the obligation)
                  effective upon written notice to ViroPharma, and to the
                  broadest extent permitted under the SaSy Agreement without
                  requiring the prior written consent of SaSy, to increase the
                  extent of its licenses and rights to permit Aventis to perform
                  any or all, at Aventis' option, of ViroPharma's development,
                  manufacturing and marketing of VP Compounds and VP Product
                  under this Agreement as follows:

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                                                                         Page 98

<PAGE>

                  (a)  To the broadest extent permitted under the SaSy Agreement
                       without requiring the prior written consent of SaSy
                       ViroPharma grants to Aventis the royalty-free, non-
                       sublicensable, except as set forth in Sections 2.3, 2.4
                       and 2.5, right and license in the Territory and in the
                       Field to use the ViroPharma Technology to make or have
                       made VP Compounds or VP Products. ViroPharma will, at
                       Aventis' request, use its commercially reasonable efforts
                       to obtain any consents necessary from SaSy to effectuate
                       the foregoing, or otherwise cooperate with Aventis in
                       effectuating any of the foregoing.

                  (b)  ViroPharma shall suspend its development, manufacturing
                       and marketing of VP Compounds and VP Product under this
                       Agreement to the extent that Aventis has selected and
                       started performing any such activities (except with
                       respect to manufacturing as may be required pursuant to
                       the SaSy Agreement).

                  (c)  Aventis shall have the sole right to perform the
                       activities it has selected and started to perform with
                       respect to development, manufacturing and marketing of VP
                       Compounds and VP Product (except with respect to
                       manufacturing as may be required pursuant to the SaSy
                       Agreement).

                  (d)  ViroPharma shall use its best efforts to maintain
                       Aventis' supply of VP Compounds or VP Products.

                  (e)  ViroPharma shall, on a Regulatory Approval-by Regulatory
                       Approval basis, and at the direction of and in
                       consultation with Aventis, use its best efforts to
                       maintain the effectiveness of such Regulatory Approvals
                       or any successors thereto.

                  (f)  ViroPharma's rights and obligations pursuant to Sections
                       8.1, 8.2, 8.3, 8.4 and 8.5 shall continue, and, in
                       addition, ViroPharma shall pay Aventis any reasonable
                       amounts by which Aventis' costs to perform any activities
                       undertaken by Aventis pursuant to this Section 12.4.3
                       exceed the amounts budgeted for such activities in the
                       applicable Development Plan and Budget or
                       Commercialization Plan and Budget, and any such
                       additional payment by ViroPharma shall not be a
                       Development Expense or Commercialization Expense. For the
                       sake of clarity, ViroPharma's obligation to pay its
                       portion of Development Expenses and Commercialization
                       Expenses shall continue under this Section 12.4.3(f).

                  (g)  Aventis acknowledges that this Section 12.4.3 in no way
                       grants to Aventis any rights under the SaSy Agreement,
                       and gives Aventis

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                                                                         Page 99

<PAGE>

                       no interest in the Intellectual Work Product, the IWP
                       Patents, the SaSy Patents, or the ViroPharma Technology,
                       except as otherwise expressly set forth in this
                       Agreement.

                  (h)  Aventis shall take no action that materially adversely
                       affects the SaSy Agreement, the SaSy Patents, the
                       ViroPharma Technology, the Intellectual Work Product, or
                       the IWP Patents.

                  (i)  The Parties agree to exert commercially reasonable
                       efforts to assure a smooth transition for any activities
                       undertaken by Aventis under this Section 12.4.3, and
                       suspended by ViroPharma pursuant to Section 12.4.3(b).

                  (j)  During the time that Aventis has expanded its right under
                       this Section 12.4.3, (x) ViroPharma's participation on
                       the JSC and any of its subcommittees shall be suspended
                       and Aventis shall be the sole participant thereon, and
                       (y) Aventis shall have a royalty-free right and license
                       (but not the obligation) under ViroPharma's rights to
                       perform all such activities no longer being performed by
                       ViroPharma.

                  (k)  If (i) the Parties obtain a final non-appealable judgment
                       regarding the Termination Challenge; (ii) there is a
                       judgment regarding the Termination Challenge that SaSy
                       and the Parties agree not to appeal; or (iii) the Parties
                       enter into a binding agreement settling the Termination
                       Challenge, in each case, as a result of which the SaSy
                       Agreement continues to be in full force and effect, then
                       the provisions of Section 12.4.3 shall cease to be in
                       effect, other than payment obligations or liabilities
                       incurred before such time.

                  The provisions of this Section 12.4.3 shall be subject to and
                  implemented in accordance with any Hart-Scott-Rodino filing
                  requirements.

          12.4.4  Suspension of Activities. If a Change of Control of ViroPharma
                  that would enable Aventis to expand temporarily its rights
                  pursuant to Section 12.4.3 does not involve a Major Company,
                  instead of temporarily expanding its rights pursuant to
                  Section 12.4.3, Aventis shall have the right (but not the
                  obligation) upon written notice to ViroPharma, to suspend its
                  promotion, Detailing and Distribution of VP Products until the
                  earlier of:

                  (a)  an agreement has been reached with SaSy permitting the
                       continued promotion, Detailing and Distribution of VP
                       Products by Aventis and ViroPharma,

                  (b)  a final, non-appealable judgment has been entered to the
                       effect that the promotion, Detailing and Distribution of
                       VP Products does not infringe SaSy's Patents in the
                       Field, or

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                                                                        Page 100

<PAGE>

                  (c)  the Parties (i) obtain a final non-appealable judgment
                       regarding the Termination Challenge; (ii) there is a
                       judgment regarding the Termination Challenge that SaSy
                       and the Parties agree not to appeal; or (iii) enter into
                       a binding agreement settling the Termination Challenge,
                       in each case, as a result of which the SaSy Agreement
                       continues to be in full force and effect.

                  During the time that Aventis has suspended any activities
                  under this Section 12.4.4, (x) Aventis' participation on the
                  JSC and any of its subcommittees shall also be suspended and
                  ViroPharma shall be the sole participant thereon, and (y)
                  ViroPharma shall have a royalty-free right and license (but
                  not the obligation) under Aventis' rights to perform all such
                  activities no longer being performed by Aventis, and Aventis
                  shall have no right to share in the Net Profits from such VP
                  Products.

          12.4.5  Resumption of Activities. Upon the occurrence of any of the
                  events described in Section 12.4.4(a-c), Aventis shall resume
                  the promotion, Detailing and Distribution of VP Products
                  suspended pursuant to Section 12.4.4 and, if ViroPharma
                  exercised its right and license to perform all activities no
                  longer being performed by Aventis, then, unless ViroPharma has
                  ceased performing commercialization activities, Aventis shall
                  pay ViroPharma an amount equal to ****** percent (******%) of
                  any reasonable amounts by which ViroPharma's costs to perform
                  any activities undertaken by ViroPharma pursuant to Section
                  12.4.4 exceed the amounts budgeted for such activities in the
                  applicable Development Plan and Budget or Commercialization
                  Plan and Budget, and any such payment by Aventis shall not be
                  a Development Expense or Commercialization Expense (the "Buy-
                  in Amount"). Payment of the Buy-in Amount shall be made
                  through Aventis' payment to ViroPharma of a percentage of the
                  amount of Net Profits from sales of VP Product due to Aventis
                  as set forth below, which paid amount shall be credited
                  against the Buy-in Amount, until the complete payment of such
                  Buy-in Amount:

                      Calendar Quarters after    Percentage of Net Profits from
                      the Occurrence of Any of     sales of VP Product due to
                      the Events Described in    Aventis Required to be Paid to
                      Section 12.4.4(a-c)                  ViroPharma
                      -------------------------  ------------------------------
                           ******                            ******%
                           ******                            ******%
                           ******                            ******%
                           ******                            ******%
                           ******                            ******%

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<PAGE>

     12.5  Aventis Put Option; ViroPharma Call Option.

           12.5.1  If at any time during the term of this Agreement there shall
                   occur a Change of Control of ViroPharma involving an Aventis
                   Competitor, then within forty-five (45) days after the date
                   of such event, Aventis may by written notice delivered to
                   ViroPharma elect to cause a valuation of the Aventis Interest
                   pursuant to Section 12.5.3. If Aventis makes such election,
                   then Aventis shall sell to ViroPharma the Aventis Interest in
                   accordance with Section 12.5.5.

           12.5.2  If at any time during the Term there shall occur a Change of
                   Control of Aventis or Aventis, S.A., involving a Person that:

                   (a)  sells a pharmaceutical product that is a direct
                        competitor of VP Product that has achieved a North
                        American market share of at least seven and one-half
                        percent (7.5%) for the Calendar Year immediately
                        preceding the Change of Control based on total
                        prescription sales, as reported in the corresponding IMS
                        ATC II or III category,

                   (b)  sells a prescription or OTC pharmaceutical product that
                        is an indirect competitor of VP Product that has
                        achieved a North American market share of at least seven
                        and one-half percent (7.5%) for the Calendar Year
                        immediately preceding the Change of Control based on
                        total sales, as reported in the corresponding IMS ATC II
                        or III category,

                   (c)  sells other prescription pharmaceutical products such
                        that VP Product was among the top ten (10) products in
                        the product portfolio of Aventis for the Calendar Year
                        immediately preceding the Change of Control based on
                        total prescription sales, as reported in the
                        corresponding IMS ATC II or III category, and VP Product
                        will not be among the top ten (10) products in the
                        product portfolio of such combined entity by Net Sales
                        for the Calendar Year immediately preceding the Change
                        of Control based on total prescription sales, as
                        reported in the corresponding IMS ATC II or III
                        category,

                   then within forty-five (45) days after the date of such
                   event, ViroPharma may by written notice delivered to Aventis
                   elect to cause a valuation of the Aventis Interest pursuant
                   to Section 12.5.3. If ViroPharma makes such election, then
                   ViroPharma shall purchase from Aventis the Aventis Interest
                   in accordance with Section 12.5.5.

           12.5.3  If Aventis elects to cause a valuation of the Aventis
                   Interest pursuant to Section 12.5.1 or ViroPharma elects to
                   cause a valuation of the Aventis Interest pursuant to Section
                   2.7.5(b), or 12.5.2, the price (the "Aventis

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                                                                        Page 102

<PAGE>

                   Interest Price") to be paid for the Aventis Interest shall be
                   conclusively determined by two internationally recognized
                   investment banking firms, one of which shall be retained and
                   paid by Aventis and one of which shall be retained and paid
                   by ViroPharma; provided that, if either Party fails to
                   deliver notice to the other Party of its selection of an
                   investment banking firm within twenty (20) days after notice
                   by the other Party that it has selected an investment banking
                   firm (which notice shall identify such firm), the
                   determination shall be rendered by the single investment
                   banking firm so selected (whose fees, in such case, shall be
                   borne equally by the Parties). Aventis and ViroPharma shall
                   promptly notify each other of its respective selections. The
                   investment banking firms selected in accordance with the
                   foregoing procedure shall each determine the fair market
                   value of the Aventis Interest as contained in written reports
                   prepared in accordance with this Section 12.5.3 and shall
                   submit their determinations of such value to Aventis and
                   ViroPharma within thirty (30) days following their selection.
                   Each value of the Aventis Interest Price determined under
                   this Section 12.5.3 for the Aventis Interest shall be an
                   amount that, on the basis of market and other conditions
                   prevailing at such time, could reasonably be expected to be
                   paid therefor by a Third Party in an arm's-length
                   transaction, assuming that the buyer and seller are under no
                   compulsion to buy or sell, it being understood and agreed
                   that all intellectual property rights and other assets
                   licensed, leased or otherwise made available by the Parties
                   and their respective Affiliates hereunder shall only be
                   valued on a going concern basis in terms of such availability
                   and use under this Agreement.

           12.5.4  The Aventis Interest Price shall be the amount equal to the
                   sum of such fair market values for the Aventis Interest
                   determined by the two (2) investment banking firms divided by
                   two (2), except that if there is more than a ten percent
                   (10%) difference between such values, a third investment
                   banking firm (which is a "top-tier" or "bulge-bracket"
                   investment banking firm) selected by the first two investment
                   banking firms (or, if the two investment banking firms are
                   unable to select such a third investment banking firm within
                   twenty (20) days following submission of the two initial
                   valuations, then the two initial investment banking firms
                   within twenty (20) days thereafter each shall submit the
                   names of three investment banking firms (each of which is a
                   "top-tier" or "bulge-bracket" investment banking firm)
                   willing to act as the third investment banking firm
                   hereunder, one of which firms shall be selected by lot by the
                   Parties) shall determine such fair market value by selecting
                   one (but only one) of the two values previously determined by
                   the first two investment banking firms pursuant to this
                   Section 12.5.4. The cost of such third investment banking
                   firm shall be borne one half (50%) by Aventis and one half
                   (50%) by ViroPharma.

           12.5.5  Any purchase and sale of the Aventis Interest pursuant to
                   this Section 12.5 shall be consummated at closing at the
                   principal offices of Aventis on a

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                                                                        Page 103

<PAGE>

                   business day within ninety (90) days following the
                   determination of the Aventis Interest Price on such date as
                   the Parties shall mutually agree; provided that such period
                   shall be extended for such period of time as shall be
                   necessary in order to obtain requisite governmental or
                   regulatory approvals with respect to such transaction. At
                   such closing, ViroPharma shall pay the Aventis Interest Price
                   by wire transfer of immediately available funds.

           12.5.6  Upon the closing of the transactions contemplated by this
                   Section 12.5, the Parties shall take all commercially
                   reasonable steps to transition the performance of Aventis'
                   obligations under this Agreement to ViroPharma and execute
                   such other documents as are necessary to transfer all of the
                   Aventis Interest in order to release Aventis from all
                   obligations under this Agreement effective as of the time of
                   such sale (except as expressly provided herein).

13.  TERM & TERMINATION.

     13.1  Term.

           13.1.1  Initial Term. The initial term of this Agreement will begin
                   on the Effective Date and, unless terminated earlier in
                   accordance with this Article 13, will extend for each VP
                   Product Exclusivity Unit, until the expiration of the
                   applicable VP Product Exclusivity Period, unless renewed
                   pursuant to Section 13.1.2 below.

           13.1.2  Renewal. For each VP Product Exclusivity Unit, the initial
                   term and any subsequent renewal terms of this Agreement shall
                   be extended by consecutive renewal terms of one year each
                   unless:

                   (a)  Aventis provides notice to ViroPharma of its intent not
                        to renew the term of this Agreement for such VP Product
                        Exclusivity Unit at least six (6) months before the date
                        of such renewal, or

                   (b)  the initial or renewal term of this Agreement is
                        terminated earlier in accordance with this Article 13.

     13.2  Restriction on Termination Right. Notwithstanding anything to the
           contrary in this Article 13, neither Party may exercise any of the
           termination rights set forth in this Article 13 if such Party is then
           in breach of this Agreement, which breach has not been timely cured
           by such Party, or waived by the other Party in writing.

     13.3  Termination for Failure to Perform Details. If a Party incurs two (2)
           Lapse Years in any consecutive three (3) Calendar Year period, and
           the other Party incurs no Lapse Year during this period, then the
           Party incurring no Lapse Years may, at its discretion, within thirty
           (30) days of confirming the occurrence of such other Party's Lapse
           Years, terminate this Agreement upon thirty (30) days written notice.

________________________________________________________________________________
                                                                        Page 104

<PAGE>

     13.4  Termination for Failure of Supply. If during the Initial Supply
           Period:

           13.4.1  for any six (6) consecutive months the number of units of
                   Finished VP Product delivered in each of such months is less
                   than ****** percent (******%) of the number of units (SKU) in
                   each Firm Order to be delivered in such month, or

           13.4.2  for any ten (10) months in any consecutive twelve (12) months
                   the number of units (SKU) of Finished VP Product delivered in
                   each of such months is less than ****** percent (******%) of
                   the number of units (SKU) in each Firm Order to be delivered
                   in each such month

           then within thirty (30) days of the occurrence of either of the
           events described in Section 13.4.1 or 13.4.2, Aventis may terminate
           this Agreement upon thirty (30) days written notice. The failure to
           supply VP Product subject to Section 6.2.2 shall not be a material
           breach of this Agreement other than for the purposes of Section 13.4
           and Aventis shall not be entitled to any damages other than those
           amounts specifically provided for in Section 6.2.2.

     13.5  Termination for Buy-Out. This Agreement shall terminate upon the
           closing date of:

           13.5.1  ViroPharma's exercise of its option under Section 2.7.5(b),
                   or

           13.5.2  either Party's exercise of its put-call rights under Section
                   12.5.

     13.6  Aventis Termination Right.

           13.6.1  Lack of Regulatory Approval. If the first Regulatory Approval
                   in the United States of an NDA for a VP Product for the First
                   Indication has not been granted before ******, Aventis may
                   terminate this Agreement by providing written notice of such
                   termination to ViroPharma not later than ******, which
                   termination shall become effective immediately upon
                   ViroPharma's receipt of such notice.

           13.6.2  Sales Based. If in Calendar Year ******, Net Sales of VP
                   Products are not at least ****** U.S. dollars (U.S. $******)
                   then no later than ******, Aventis may terminate this
                   Agreement by providing written notice of such termination to
                   ViroPharma, which termination shall become effective one
                   hundred eighty (180) days after such notice. Thereafter, if
                   Net Sales of VP Product in any Calendar Year set forth below
                   are not at least the corresponding amounts set forth below
                   then at any time in the January immediately following such
                   Calendar Year, Aventis may terminate this Agreement by
                   providing written notice of such termination to ViroPharma,
                   which termination shall become effective one hundred eighty
                   (180) days after such notice:
________________________________________________________________________________
                                                                        Page 105
<PAGE>

                    Calendar                Net Sales of VP Product Below
                    Year                    Which Termination Right is Triggered
                    ----                    ------------------------------------
                    ******                             U.S. $******
                    ******                             U.S. $******
                    ******                             U.S. $******

           13.6.3   Other. If at any time during this Agreement any of the
                    following events occurs, Aventis may terminate this
                    Agreement at any time during the sixty (60) day period after
                    such event first occurs by providing written notice of such
                    termination to ViroPharma, which termination shall become
                    effective one hundred eighty (180) days after such notice:

                    (a)  FDA requires that the labeling for VP Product contain a
                         boxed warning relating to a serious hazard associated
                         with the use of VP Product;

                    (b)  Either (i) FDA withdraws Regulatory Approval of an NDA
                         for VP Product, for reasons of safety or efficacy, or
                         (ii) ViroPharma withdraws an NDA for, or either of the
                         Parties ceases the marketing of, a VP Product under the
                         reasonable threat of, or to avoid an, FDA withdrawal of
                         the Regulatory Approval of the applicable NDA, for
                         reasons of safety or efficacy.

     13.7  Consequences of Breach.

           13.7.1   Generally. This Agreement may be terminated effective
                    immediately by written notice by either Party at any time
                    during the term of this Agreement for breach by the other
                    Party of any material representation, warranty, covenant or
                    agreement set forth herein, which breach remains uncured for
                    thirty (30) days in the case of nonpayment of any amount due
                    (unless there exists a bona fide dispute as to whether such
                    payment is owing, in which case the thirty (30) day period
                    shall begin on the resolution of such dispute) and thirty
                    (30) days for all other breaches, as may be extended by the
                    non-breaching Party, each measured from the date written
                    notice of such breach is given to the breaching Party;
                    provided, however, that if such breach is not susceptible of
                    cure within the stated period and the breaching Party uses
                    diligent good faith efforts to cure such breach, the stated
                    period will be extended by an additional thirty (30) days.
                    In the case of an Uncurable ViroPharma Breach, Section
                    13.7.3(b) shall apply.

           13.7.2   Exception. The failure of a Party to perform PDEs or Details
                    assigned to it shall not be a material breach of this
                    Agreement other than for the purposes of Section 13.2.
________________________________________________________________________________
                                                                        Page 106
<PAGE>

           13.7.3   Aventis Alternative Right upon ViroPharma Breach. In lieu of
                    exercising the right of termination set forth in Section
                    13.7.1 and seeking damages:

                    (a)  Curable ViroPharma Breach. In its sole discretion,
                         Aventis shall have the right (but not the obligation),
                         to the extent possible, to cure any Curable ViroPharma
                         Breach that remains uncured following the cure
                         period(s) set forth in Section 13.7.1. In furtherance
                         of the foregoing, to the broadest extent permitted
                         under the SaSy Agreement without requiring the prior
                         written consent of SaSy, ViroPharma hereby grants to
                         Aventis any and all rights and non-exclusive licenses
                         necessary in order for Aventis to cure such breach or
                         alleged breach. Aventis shall charge the actual amounts
                         reasonably incurred by it in curing such breach to its
                         Development Account or Commercialization Account (the
                         "Cure Amount"), as appropriate, and in addition
                         ViroPharma shall pay Aventis an amount equal to ******,
                         which shall not be charged to either Party's
                         Development Account or Commercialization Account.

                    (b)  Uncurable ViroPharma Breach or Multiple Curable
                         ViroPharma Breaches; Expansion of Aventis Rights. In
                         the event of an Uncurable ViroPharma Breach or ******
                         Curable ViroPharma Breaches in any ****** for each of
                         which Aventis exercises its right pursuant to Section
                         13.7.3(a), Aventis may elect by written notice to
                         ViroPharma that, to the broadest extent permitted under
                         the SaSy Agreement without requiring the prior written
                         consent of SaSy:

                         (i)   ViroPharma grants to Aventis the royalty-free,
                               non-sublicensable, except as set forth in
                               Sections 2.3, 2.4 and 2.5, right and license in
                               the Territory and in the Field to use the
                               ViroPharma Technology to make or have made VP
                               Compounds or VP Products, which right shall be
                               exclusive, except to the extent required to
                               fulfill the intent of Section 13.7.3(b)(ii) or
                               13.7.3(b)(iii) even as to ViroPharma and its
                               Affiliates. ViroPharma will, at Aventis' request,
                               use its commercially reasonable efforts to obtain
                               any consents necessary for SaSy to effectuate the
                               foregoing, or otherwise cooperate with Aventis in
                               effectuating any of the foregoing.

                         (ii)  ViroPharma shall suspend researching, developing,
                               manufacturing or commercializing VP Compounds and
                               VP Products (except with respect to manufacturing
                               as may be required pursuant to the SaSy
                               Agreement).

                         (iii) Aventis shall have the sole right to perform any
                               of the activities performed by either Party
                               pursuant to this
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                                                                        Page 107
<PAGE>

                               Agreement with respect to VP Compounds and VP
                               Products under the Agreement (except with respect
                               to manufacturing as may be required pursuant to
                               the SaSy Agreement).

                         (iv)  ViroPharma shall, on an agreement-by-agreement
                               basis, either (i) assign to Aventis agreements
                               relating to the supply of VP Compounds or VP
                               Products or (ii) use its best efforts to maintain
                               Aventis' supply of VP Compounds of VP Products,
                               and in each case Aventis shall grant to
                               ViroPharma a license to make or have made VP
                               Compounds or VP Products solely to the extent
                               required to achieve the purposes of this clause
                               (iv).

                         (v)   ViroPharma shall, on a Regulatory Approval-by
                               Regulatory Approval basis, and at the direction
                               of and in consultation with Aventis, either (i)
                               assign to Aventis Regulatory Approvals concerning
                               VP Compounds and VP Products as soon as practical
                               and at ViroPharma's expense or (ii) use its best
                               efforts to maintain the effectiveness of such
                               Regulatory Approvals or any successors thereto.

                         (vi)  From and after the date Aventis exercises its
                               right pursuant to this Section 13.7.3(b),
                               ViroPharma's rights to receive payments pursuant
                               to Sections 8.1, 8.2, 8.3, 8.4, and 8.5 shall
                               continue, and Aventis shall charge the actual
                               incremental amounts reasonably incurred by it in
                               performing the development and commercialization
                               activities previously allocated to ViroPharma to
                               its Development Account or Commercialization
                               Account (the "Replacement Amount"), as
                               appropriate, and in addition ViroPharma shall pay
                               Aventis an amount equal to the Replacement
                               Amount, which shall not be charged to either
                               Party's Development Account or Commercialization
                               Account. For the sake of clarity, ViroPharma's
                               obligation to pay its portion of Development
                               Expenses and Commercialization Expenses shall
                               continue under this Section 13.7.3(b).

                         (vii) Aventis acknowledges that this Section 13.7.3 in
                               no way grants to Aventis any rights under the
                               SaSy Agreement, and gives Aventis no interest in
                               the Intellectual Work Product, the IWP Patents,
                               the SaSy Patents, or the ViroPharma Technology,
                               except as otherwise expressly set forth in this
                               Agreement.
________________________________________________________________________________
                                                                        Page 108
<PAGE>

                         (viii)  Aventis shall take no action that materially
                                 adversely affects the SaSy Agreement, the SaSy
                                 Patents, the ViroPharma Technology, the
                                 Intellectual Work Product, or the IWP Patents.

                         (ix)    During the time that Aventis has expanded its
                                 right under this Section 13.7.3, (x)
                                 ViroPharma's participation on the JSC and any
                                 of its subcommittees shall be suspended and
                                 Aventis shall be the sole participant thereon,
                                 and (y) Aventis shall have a royalty-free right
                                 and license (but not the obligation) under
                                 ViroPharma's rights to perform all such
                                 activities no longer being performed by
                                 ViroPharma.

     13.8  Termination for Insolvency. To the extent permitted by Law, either
           Party may terminate this Agreement if, at any time, the other Party
           shall file in any court or agency pursuant to any statute or
           regulation of any state or country, a petition in bankruptcy or
           insolvency or for reorganization or for an arrangement or for the
           appointment of a receiver or trustee of the Party or of its assets,
           or if the other Party proposes a written agreement of composition or
           extension of its debts, or if the other Party shall be served with an
           involuntary petition against it, filed in any insolvency proceeding,
           and such petition shall not be dismissed within sixty days after the
           filing thereof, or if the other Party shall propose or be a party to
           any dissolution or liquidation, or if the other Party shall make an
           assignment for the benefit of creditors.

     13.9  Termination of the SaSy Agreement. This Agreement shall automatically
           terminate upon the termination or expiration of the SaSy Agreement
           for any reason.

     13.10 General Consequences of Termination or Expiration. Upon the
           expiration or termination of this Agreement for any reason, except as
           otherwise limited by Laws:

           13.10.1  Survival of Accrued Rights. The rights of either Party
                    against the other accrued or accruing under this Agreement
                    or under Laws before termination, including, without
                    limitation, the obligations to pay any amounts, and the
                    consequences resulting from the termination of the SaSy
                    Agreement shall be unaffected.

          13.10.2   Licenses. The Party which is ceasing selling and promoting
                    VP Product hereby grants to the other Party for the
                    Territory, for the period terminating immediately upon the
                    earlier of (i) such other Party's Distribution of all the VP
                    Product in its possession on the date of expiration or
                    termination of this Agreement or (ii) one (1) year from the
                    date of expiration or termination of this Agreement, a non-
                    exclusive, limited, royalty-free license under the granting
                    Party's rights to its name and logo to the extent the such
                    name and logo is incorporated in any
________________________________________________________________________________
                                                                        Page 109
<PAGE>

                    Promotional Materials or the labeling for any VP Product
                    solely to the extent reasonably necessary for the other
                    Party to distribute such VP Product and such Promotional
                    Materials in connection with selling and promoting VP
                    Product.

           13.10.3  Return of Confidential Information. Subject to the terms of
                    Article 11, each Party shall destroy and shall not retain
                    any copies of the other Party's Confidential Information,
                    except for one copy to be retained by legal counsel solely
                    for archival purposes.

           13.10.4  Return of Materials. Aventis shall within thirty (30) days
                    of such termination or expiration deliver to ViroPharma all
                    VP Product, Samples, Promotional Materials, communications
                    materials, marketing plans and reports and other materials
                    related to the Promotion of VP Product.

     13.11 Continuing Obligations. Upon termination or expiration of this
           Agreement for any reason, the provisions of the following Articles
           and Sections 7.4.1(c), 7.5, 7.6, 8.11, 10.1, 10.4, 11, 13.10, 13.11,
           14.2.13, 14.3.5, 14.4, 15.1, 15.2, 15.4, 15.6, 17.2, 17.6, 17.9,
           17.11shall survive in accordance with their respective terms without
           limitation; it being further understood and agreed that the rights
           and obligations of a Party with respect to any breach of this
           Agreement, including, without limitation, any breach of this
           Agreement resulting in the termination of the SaSy Agreement, or any
           termination of the SaSy Agreement due to a Change of Control of
           ViroPharma, prior to such termination of this Agreement shall survive
           termination of this Agreement without limitation.

14.  REPRESENTATIONS, WARRANTIES & COVENANTS.

     14.1  Representations, Warranties of Each Party. As of the Effective Date,
           each of ViroPharma and Aventis hereby represents, warrants, and
           covenants to the other Party hereto as follows:

           14.1.1   It is a corporation or entity duly organized and validly
                    existing under the laws of the state or other jurisdiction
                    of its incorporation or formation.

           14.1.2   The execution, delivery and performance of this Agreement by
                    such Party has been duly authorized by all requisite
                    corporate action and does not require any shareholder action
                    or approval or the consent of any Third Party.

           14.1.3   It has the power and authority to execute and deliver this
                    Agreement and to perform its obligations hereunder.

           14.1.4   The execution, delivery and performance by such Party of
                    this Agreement and its compliance with the terms and
                    provisions hereof does not and will not conflict with or
                    result in a breach of any of the terms and provisions of or
                    constitute a default under: (a) a loan agreement, guaranty,
                    financing agreement, or other agreement or instrument
                    binding or affecting it or its
________________________________________________________________________________
                                                                        Page 110
<PAGE>

                    property; (b) the provisions of its charter or operative
                    documents or bylaws; or (c) any Laws, order, writ,
                    injunction or decree of any court or governmental authority
                    entered against it or by which any of its property is bound.

          14.1.5    As of the Effective Date, there are no actions, suits,
                    proceedings or claims, pending against it or any of its
                    Affiliates, or, to the best of its knowledge, threatened
                    against it or any of its Affiliates, at law or in equity, or
                    before or by any court or Regulatory Authority relating,
                    directly or indirectly, to any of the matters contemplated
                    under this Agreement, or to the research, development,
                    marketing or sale of any of its pharmaceutical products. To
                    the best of its knowledge, there are no investigations,
                    pending or threatened against it or any of its Affiliates,
                    at law or in equity, or before or by any Regulatory
                    Authority relating, directly or indirectly, to the matters
                    contemplated under this Agreement, or to the research,
                    development, marketing or sale of any of its pharmaceutical
                    products, or which would otherwise materially adversely
                    affect its ability to perform its obligations hereunder.

          14.1.6    It shall use commercially reasonable diligence in performing
                    all of the activities under this Agreement.

          14.1.7    It shall at all times comply with all applicable Laws
                    relating to its activities under this Agreement.

          14.1.8    It has the full right, power and authority to grant all of
                    the right, title and interest in the licenses granted to the
                    other Party under this Agreement.

     14.2 ViroPharma Representations, Warranties and Covenants. ViroPharma
          hereby represents, warrants, covenants and agrees as follows:

          14.2.1    As of the Effective Date hereof, Exhibit 1.81 contains a
                    correct and complete list of all Patents issued or pending
                    in the Territory relating to Pleconaril that are licensed to
                    ViroPharma from SaSy. Exhibit 1.100 contains a correct and
                    complete list of all ViroPharma Patents issued or pending in
                    the Territory. To the best of ViroPharma's knowledge, all of
                    the Patents listed in Exhibits 1.81 and 1.100 issued as of
                    the date hereof are valid and in full force.

          14.2.2    As of the date hereof, to the best of ViroPharma's
                    knowledge, the manufacture, use or sale of (a) VP Compounds
                    or (b)the VP Product formulation for which NDA 21-245 was
                    submitted to the FDA on July 31, 2001 will not infringe any
                    valid, enforceable Third Party Patents. ViroPharma makes no
                    representation or warranty as to any Combination Product, or
                    as to the use of VP Compound or of the VP Product
                    formulation for which NDA 21-245 was submitted to the FDA on
                    July 31, 2001, in combination with other ingredients.
________________________________________________________________________________
                                                                        Page 111
<PAGE>

          14.2.3    ViroPharma agrees to comply with and observe in all material
                    respects its obligations under the SaSy Agreement.

          14.2.4    ViroPharma agrees not to terminate or amend or otherwise
                    modify or waive any of the terms of the SaSy Agreement in
                    any way adversely affecting Aventis' rights under this
                    Agreement without the prior written consent of Aventis.

          14.2.5    Other than as may be due under the SaSy Agreement, as of the
                    Effective Date, no other Royalties would be payable by
                    ViroPharma to any other Third Party with respect to the sale
                    of any VP Product if sales of VP Products were to take place
                    on the Effective Date.

          14.2.6    The ViroPharma Technology that ViroPharma owns is owned free
                    from any material liens or restrictions, except as otherwise
                    set forth in the SaSy Agreement.

          14.2.7    The SaSy Agreement is in full force and effect in accordance
                    with its terms, and is free and clear of any material liens
                    or restrictions, except for those set forth in the SaSy
                    Agreement, and except where the failure to be free from such
                    liens or restrictions would not materially and adversely
                    affect the ability of ViroPharma to conduct its business as
                    presently conducted or proposed to be conducted hereunder.

          14.2.8    There is no claim or demand of any person or entity
                    pertaining to, or any proceeding which is pending or, to the
                    knowledge of ViroPharma, threatened, that challenges the
                    rights of ViroPharma in respect of any ViroPharma
                    Technology, or that claims that any default exists under any
                    license with respect to ViroPharma Technology to which
                    ViroPharma is a party, except where such claim, demand or
                    proceeding would not materially and adversely affect the
                    ability of ViroPharma to carry out its obligations under
                    this Agreement.

          14.2.9    Other than confidentiality agreements and a letter agreement
                    dated March 1998 in respect of amounts due SaSy under the
                    predecessor agreement to the SaSy Agreement , the SaSy
                    Agreement is the only oral or written contract or agreement
                    between ViroPharma or any of its Affiliates on the one hand,
                    and SaSy or any of its Affiliates on the other hand.
                    ViroPharma is not in default or breach of the SaSy
                    Agreement, nor has it received any notice of any defaults,
                    breaches or violation thereunder. To the best of
                    ViroPharma's knowledge, SaSy is not in default or breach of
                    the SaSy Agreement.

          14.2.10   With respect to each submission to the FDA or other
                    Regulatory Authority regarding a VP Compound or VP Product,
                    neither ViroPharma, nor any officer, employee or agent of
                    ViroPharma has made an untrue statement of a material fact
                    or fraudulent statement to the FDA or other Regulatory
________________________________________________________________________________
                                                                        Page 112
<PAGE>

                    Authority, or knowingly failed to disclose a material fact
                    required to be disclosed to any Regulatory Authority.

          14.2.11   Each unit of Finished VP Product delivered to Aventis
                    pursuant to this Agreement will:

                    (a)  Be manufactured, packaged, tested, stored, and shipped
                         by ViroPharma in conformance with Laws, including,
                         without limitation, with all applicable regulations of
                         the FDA,

                    (b)  Meet specifications for such Finished VP Product
                         applicable at the time of receipt of such Finished VP
                         Product by Aventis,

                    (c)  Not be adulterated within the meaning of the FD&C Act,
                         and not be an article which may not under the
                         provisions of the FD&C Act be introduced into
                         interstate commerce, at the time of delivery of such
                         Finished VP Product to Aventis,

                    (d)  Be free and clear of all liens, security interests and
                         other encumbrances at the time of receipt of such
                         Finished VP Product by Aventis;

          14.2.12   The documents delivered or made available by ViroPharma to
                    Aventis or their attorneys or agents in connection the
                    transactions contemplated hereby do not contain any untrue
                    statement of a material fact nor, to ViroPharma's knowledge,
                    omit to state a material fact necessary in order to make the
                    statements contained herein or therein, in light of the
                    circumstances under which such statements were made, not
                    misleading. To ViroPharma's knowledge, there are no facts
                    that (individually or in the aggregate) materially adversely
                    affect the transactions contemplated hereby that have not
                    been made available to Aventis or their attorneys or agents
                    in connection herewith.

          14.2.13   Upon termination of the SaSy Agreement as a result of a
                    Change in Control, or as a result of a breach of the SaSy
                    Agreement caused by ViroPharma, ViroPharma hereby covenants
                    and agrees that, for a period of three years following the
                    termination of the SaSy Agreement, it shall not enter into
                    any agreement with SaSy or its Affiliates relating to, and
                    shall not otherwise develop, promote for sale, or sell a VP
                    Product or VP Compound in the Territory, in the Field.

          14.2.14   ViroPharma shall negotiate with Aventis or any of its
                    Affiliates in good faith and on an exclusive basis for
                    ninety (90) days after the Effective Date an agreement
                    regarding the commercialization of VP Compounds and VP
                    Product in Canada.

     14.3 Aventis' Representations, Warranties and Covenants. Aventis hereby
          represents, warrants, covenants and agrees as follows:
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                                                                        Page 113
<PAGE>

          14.3.1    As of the Effective Date hereof, to the best of Aventis'
                    knowledge, there are no Aventis Patents that contain claims
                    or could contain claims that would be infringed by using,
                    selling, offering for sale, making, having made, importing
                    or exporting any VP Compound or the VP Product formulation
                    for which NDA 21-245 was submitted to the FDA on July 31,
                    2001.

          14.3.2    As of the date on which Aventis selects the Aventis Product,
                    to the best of Aventis' knowledge, the manufacture, use or
                    sale of the Aventis Product does not infringe any patents of
                    Third Parties.

          14.3.3    Aventis shall comply with ViroPharma's reasonable
                    instructions to ensure compliance with ViroPharma's
                    obligations under the SaSy Agreement.

          14.3.4    Neither Aventis nor any of its Affiliates is a party to or
                    otherwise bound by any oral or written contract or agreement
                    that will result in any Person obtaining any interest in, or
                    that would give to any Person any right to assert any claim
                    in or with respect to, any of Aventis' rights under this
                    Agreement.

          14.3.5    Upon termination of the SaSy Agreement (a) as a result of a
                    Change in Control of ViroPharma which occurs after the date
                    on which (i) Aventis, (ii) any entity which controls (within
                    the meaning of Section 1.4) Aventis or (iii) any of its
                    Affiliates that is a sublicensee or assignee of all or
                    substantially all of Aventis' rights or obligations under
                    this Agreement, becomes an Affiliate of SaSy or any of
                    SaSy's Affiliates, or (b) as a result of a breach of the
                    SaSy Agreement caused by Aventis, Aventis hereby covenants
                    and agrees that, for a period of three years following the
                    termination of the SaSy Agreement, neither Aventis nor any
                    of its Affiliates shall enter into any agreement with SaSy
                    or its Affiliates relating to, nor shall Aventis or its
                    Affiliates otherwise develop, make, have made, promote for
                    sale, or sell a VP Product or VP Compound in the Territory,
                    in the Field.

          14.3.6    Aventis shall make commercially reasonable efforts to retain
                    ownership or Control of the right to permit ViroPharma to
                    promote or Detail any Aventis Product.

          14.3.7    The Aventis Technology that Aventis owns is owned free and
                    clear from any material lien or restriction.

          14.3.8    There is no claim or demand of any person or entity
                    pertaining to, or any proceeding which is pending or, to the
                    knowledge of Aventis, threatened, that challenges the rights
                    of Aventis in respect of any Aventis Technology, or that
                    claims that any default exists under any license with
                    respect to Aventis Technology to which Aventis is a party,
                    except where such claim,
________________________________________________________________________________
                                                                        Page 114
<PAGE>

                    demand or proceeding would not materially and adversely
                    affect the ability of Aventis to carry out its obligations
                    under this Agreement.

          14.3.9    Aventis shall exercise commercially reasonable efforts to
                    assist in causing Aventis S.A. or such other Affiliate, to
                    enter into an agreement with ViroPharma within the ninety
                    (90) day period contemplated by Section 14.2.14 regarding
                    the commercialization of VP Compounds and VP Product in
                    Canada.

     14.4 Disclaimer. THE WARRANTIES OF EACH PARTY IN THIS ARTICLE 14 ARE IN
          LIEU OF ANY OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING, WITHOUT
          LIMITATION, ANY IMPLIED WARRANTIES OF NONINFRINGEMENT, ANY IMPLIED
          WARRANTIES OF MERCHANTABILITY OR ANY IMPLIED WARRANTIES OF FITNESS FOR
          A PARTICULAR PURPOSE ALL OF WHICH ARE HEREBY SPECIFICALLY EXCLUDED AND
          DISCLAIMED.

15.  INDEMNIFICATION & INSURANCE.

     15.1 Indemnification of Aventis. ViroPharma shall indemnify, defend and
          hold harmless Aventis, its Affiliates, and each of its and their
          respective employees, officers, directors and agents (the "Aventis
          Indemnitees") from and against any and all liability, loss, damages,
          expense (including reasonable attorneys' fees and expenses) and costs
          that the Aventis Indemnitee may be required to pay one or more Third
          Parties not including Aventis Indemnitees, and in the case of Section
          15.1.3, half of such costs, resulting from or arising out of:

          15.1.1  any misrepresentation or breach of any representation,
                  warranty, covenant or agreement made by ViroPharma in this
                  Agreement;

          15.1.2  any act or omission of negligence, recklessness or willful
                  misconduct of ViroPharma or any of its Affiliates;

          15.1.3  death or bodily injury resulting from the use of VP Product
                  that is in fact manufactured in accordance with Laws, and with
                  the applicable specifications for such VP Product in effect at
                  the time of manufacture, to the extent not resulting from the
                  events set forth in Section 15.1.1-2;

          15.1.4  the infringement of any Third Party issued patent rights in
                  existence as of the Effective Date in the Territory based on
                  (a) the use of VP Compound, including the use of VP Compound
                  in connection with the sale of a Combination Product, but not
                  to the extent that the claim of infringement alleges use of
                  the VP Compound in connection with any other Compound or
                  product, or (b) the use, Detailing or Distribution of the VP
                  Product formulation for which NDA 21-245 was submitted to the
                  FDA on July 31, 2001, in each case, except to the extent that
                  the activities causing infringement are based on Intellectual
                  Work Product hereunder; and
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                                                                        Page 115
<PAGE>

           15.1.5  death or bodily injury resulting from the failure of VP
                   Product to be manufactured in accordance with Laws, and with
                   the applicable specifications for such VP Product in effect
                   at the time of manufacture, except to the extent that Aventis
                   has exercised its rights in respect of manufacturing under
                   Sections 12.4.3(c) or 13.7.3,

           except, in each case, to the extent caused by any act or omission of
           negligence, recklessness or willful misconduct of any of the Aventis
           Indemnitees.

     15.2  Indemnification of ViroPharma. Aventis shall indemnify, defend and
           hold harmless ViroPharma, its Affiliates, and each of its and their
           respective employees, officers, directors and agents (the "ViroPharma
           Indemnitees") from and against any and all liability, loss, damages,
           expense (including reasonable attorneys' fees and expenses) and costs
           that the ViroPharma Indemnitee may be required to pay one or more
           Third Parties not including ViroPharma Indemnitees, and in the case
           of Section 15.2.3, half of such costs, resulting from or arising out
           of:

           15.2.1  any misrepresentation or breach of any representation,
                   warranty, covenant or agreement made by Aventis in this
                   Agreement;

           15.2.2  any act or omission of negligence, recklessness or willful
                   misconduct of Aventis or any of its Affiliates;

           15.2.3  death or bodily injury resulting from the use of VP Product
                   that is in fact manufactured in accordance with Laws, and
                   with the applicable specifications for such VP Product in
                   effect at the time of manufacture, to the extent not
                   resulting from the events set forth in Section 15.2.1-2;

           15.2.4  the infringement of any Third party issued patent rights in
                   existence as of the Effective Date in the Territory based on
                   the use, Detailing or Distribution of the Aventis Product;
                   and

           15.2.5  death or bodily injury resulting from the failure of Aventis
                   Product to be manufactured in accordance with Laws, and with
                   the applicable specifications in effect at the time of
                   manufacture,

           15.2.6  with respect to any VP Product manufactured by or on behalf
                   of Aventis during any period during which Aventis has
                   exercised its rights in respect of manufacturing under
                   Sections 12.4.3(c) or 13.7.3, death or bodily injury
                   resulting from the failure of VP Product to be manufactured
                   in accordance with Laws, and with the applicable
                   specifications for such VP Product in effect at the time of
                   manufacture, except to the extent that

           except, in each case, to the extent caused by any act or omission of
           negligence, recklessness or willful misconduct of any of the
           ViroPharma Indemnitees.

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                                                                        Page 116
<PAGE>

     15.3  Procedure for Indemnification.

           15.3.1  Notice. Each Party will notify promptly the other if it
                   becomes aware of a Third Party claim (a "Third Party Claim")
                   for which indemnification may be sought hereunder and will
                   give such information with respect there as the other Party
                   shall reasonably request. If any proceeding (including any
                   governmental investigation) is instituted involving any Party
                   regarding which indemnity may be sought pursuant to this
                   Article 15, such Party (the "Indemnified Party") shall not
                   make any admission concerning such claim, but shall promptly
                   notify the other Party (the "Indemnifying Party") in writing
                   and the Indemnifying Party and Indemnified Party shall meet
                   to discuss how to respond to any claims that are the subject
                   matter of such proceeding. The Indemnifying Party shall not
                   be obligated to indemnify the Indemnified Party to the extent
                   any admission made by the Indemnified Party or any failure by
                   such Party to notify the Indemnifying Party of the claim
                   materially prejudices the defense of such claim.

           15.3.2  Defense of Claim. If the Indemnifying Party elects to defend
                   a Third Party Claim pursuant to Section 15.3.1, it shall give
                   notice to the Indemnified Party within fifteen (15) days
                   after the receipt of the notice from the Indemnified Party of
                   the potential indemnifiable claim which involves (and
                   continues to involve) solely monetary damages; provided, that
                   (a) the Indemnifying Party expressly agrees in such notice
                   that, as between the Indemnifying Party and the Indemnified
                   Party, the Indemnifying Party shall be solely obligated to
                   satisfy and discharge the Third Party Claim, subject to the
                   terms, conditions and limitations of this Agreement (the
                   "Litigation Conditions"), and (b) the Indemnifying Party has
                   the ability, whether though its own resources or insurance to
                   satisfy the full amount of any adverse monetary judgment that
                   may result such conditions, the "Litigation Conditions").
                   Subject to compliance with the Litigation Conditions, the
                   Indemnifying Party shall retain counsel reasonably
                   satisfactory to the Indemnified Party to represent the
                   Indemnified Party and shall pay the fees and expenses of such
                   counsel related to such proceeding. In any such proceeding,
                   the Indemnified Party shall have the right to retain its own
                   counsel, but the fees and expenses of such counsel shall be
                   at the expense of the Indemnified Party unless: (a) the
                   Indemnifying Party and the Indemnified Party shall have
                   mutually agreed to the retention of such counsel, or (b) the
                   named parties to any such proceeding (including any impleaded
                   parties) include both the Indemnifying Party and the
                   Indemnified Party and representation of both Parties by the
                   same counsel would be inappropriate due to actual or
                   potential differing interests between them. All such fees and
                   expenses shall be reimbursed as they are incurred. If the
                   Litigation Conditions are not satisfied within thirty (30)
                   days after notice of the Third Party Claim was provided to
                   the Indemnifying Party, then the Indemnified Party shall have
                   the right to control the defense of such Third Party Claim
                   and the Indemnifying Party shall have the right to
                   participate in such defense at

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                                                                        Page 117
<PAGE>

                   the Indemnifying Party's own expense. The Indemnified Party
                   shall not settle any claim for which it is seeking
                   indemnification without the prior consent of the Indemnifying
                   Party which consent shall not be unreasonably withheld,
                   delayed or conditioned. The Indemnified Party shall, if
                   requested by the Indemnifying Party, cooperate in all
                   reasonable respects in the defense of such claim that is
                   being managed and controlled by the Indemnifying Party. The
                   Indemnifying Party shall not, without the written consent of
                   the Indemnified Party (which consent shall not be
                   unreasonably withheld), effect any settlement of any pending
                   or threatened proceeding in respect of which the Indemnified
                   Party is, or arising out of the same set of facts could have
                   been, a Party and indemnity could have been sought hereunder
                   by the Indemnified Party, unless such settlement includes an
                   unconditional release of the Indemnified Party from all
                   liability on claims that are the subject matter of such
                   proceeding.

     15.4  Right to Counsel. Notwithstanding anything to the contrary contained
           herein, an Indemnified Party shall be entitled to assume the defense
           of any Third Party Claim with respect to the Indemnified Party, upon
           written notice to the Indemnifying Party pursuant to this Section
           15.4, in which case the Indemnifying Party shall be relieved of
           liability under Section 15.1 or 15.2, as applicable, solely for such
           Third Party Claim.

     15.5  Insurance. Each Party shall obtain and maintain, at its sole cost and
           expense, during the term of this Agreement, Commercial General
           Liability Insurance, including Products Liability Insurance, with
           reputable and financially secure insurance carriers to cover its
           indemnification obligations under Sections 15.1 or 15.2, as
           applicable, with limits of not less than (a) in the case of
           ViroPharma, (i) prior to the Launch Date, six million dollars
           ($6,000,000) per occurrence and in the aggregate and (ii) from and
           after the Launch Date, twenty-five million dollars ($25,000,000) per
           occurrence and fifty million dollars ($50,000,000) in the aggregate
           and (b) in the case of Aventis, twenty-five million dollars
           ($25,000,000) per occurrence and fifty million dollars ($50,000,000)
           in the aggregate. Each Party shall, upon the other Party's reasonable
           request from time to time, produce evidence that such insurance
           policies are valid, kept up to date and in full force and effect and
           are kept in accordance with any local insurance laws or regulations
           from time to time in force. A Party's liability to the other is in no
           way limited to the extent of the Party's insurance coverage. In the
           event of duplicate coverage, the insurance policy of the Party whose
           fault causes the need for reimbursement under an insurance policy
           shall be primary and the other Party's secondary. Notwithstanding the
           foregoing, Aventis may satisfy its obligations under this Section
           15.5 through self-insurance to the same extent.

     15.6  Limitation. NOTWITHSTANDING ANY PROVISION OF THIS AGREEMENT TO THE
           CONTRARY, IN NO EVENT SHALL EITHER PARTY, ITS DIRECTORS, TRUSTEES,
           OFFICERS, EMPLOYEES, AGENTS OR AFFILIATES BE LIABLE TO THE OTHER
           PARTY FOR ANY INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,

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                                                                        Page 118
<PAGE>

          WHETHER BASED UPON A CLAIM OR ACTION OF CONTRACT, WARRANTY,
          NEGLIGENCE, STRICT LIABILITY OR OTHER TORT, OR OTHERWISE, ARISING OUT
          OF THIS AGREEMENT, EXCEPT TO THE EXTENT ACTUALLY PAID BY A PARTY
          PURSUANT TO A THIRD PARTY CLAIM IN ACCORDANCE WITH THIS AGREEMENT.

16.  ARBITRATION.

     16.1  General. If the Parties are unable to resolve any dispute within
           twenty (20) days of its being referred for resolution in accordance
           with Section 3.10.4, then, in accordance with Section 3.10.5, either
           Party may submit the dispute to final and binding confidential
           arbitration by filing a demand for arbitration with the other Party.
           Except for actions seeking emergency or preliminary injunctive
           relief, arbitration shall be the sole and exclusive method for
           resolving any dispute, controversy or claim arising out of or
           relating to any dispute that is not resolved pursuant to Section
           3.10.4. If a Party does move for emergency or preliminary injunctive
           relief, that Party shall also begin arbitration in accordance with
           this Article 16 so as to permit the prompt resolution of the merits
           of the dispute in arbitration after a court resolves the petition for
           emergency or temporary relief. Notwithstanding anything else
           contained herein to the contrary, the Parties hereto agree that the
           dispute resolutions set forth herein shall not apply to (a) the
           disputes listed in Section 3.10.6, (b) any claim by a Party that the
           other breached any representation, warranty, covenant or agreement
           contained herein or (c) any claim for indemnification under Article
           15.

     16.2  Notice. In no event may a demand for arbitration be filed more than
           one year after the date the claim, dispute, controversy, or other
           matter in question first arose, or more than ninety (90) days after
           the claim, dispute, controversy, or other matter in question was
           first referred for resolution pursuant to Section 3.10.4. If a demand
           for arbitration is not timely filed, the claim, dispute, controversy,
           or other matter in question referenced in the demand shall be deemed
           released, waived, barred, and unenforceable for all time, and barred
           as if by statute of limitations. Unless otherwise advised in writing,
           notice shall be addressed as provided for notices under the
           Agreement.

     16.3  Procedures for Arbitration.  The arbitration shall be conducted in
           accordance with the following procedures:

           16.3.1  Selection of Arbitrator(s).

                   (a)  The Parties shall attempt to agree on a single
                        arbitrator within fifteen (15) days of the demand for
                        arbitration.

                   (b)  If the Parties fail to agree on a single arbitrator
                        within the fifteen (15) days set forth in Section
                        16.3.1(a), then within ten (10) further

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                                                                        Page 119
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                        days each Party shall select a single arbitrator, who
                        shall together within ten (10) further days select a
                        third arbitrator.

               The single arbitrator, or the three arbitrators selected in
               accordance with this Section 16.3.1 shall preside over the
               arbitration.  Before any proceedings hereunder, the Parties shall
               obtain the agreement of the arbitrator(s) to maintain in
               confidence the substance and result of arbitration hereunder, and
               any materials disclosed under arbitration hereunder.

       16.3.2  Location, Language and Timing. Unless otherwise agreed by the
               Parties within fifteen (15) days of the demand for arbitration,
               the arbitration shall take place in the English language in
               Philadelphia, Pennsylvania, within sixty (60) days of when the
               arbitrator(s) are appointed. The arbitration hearing shall be
               held on consecutive business days without interruption to the
               maximum extent practicable.

       16.3.3  Evidence, Exhibits, Depositions and Discovery. Each Party shall
               provide the other Party with a list of exhibits, witnesses, and
               expert witnesses, if any, at least thirty (30) days before the
               arbitration hearing. Either Party may take no more than two (2)
               depositions in addition to any witness identified by the other
               Party. Unless otherwise agreed to by the Parties, no other
               discovery shall be permitted. Charts, graphs, and summaries shall
               be used to present voluminous data, provided that the underlying
               data is made available to the opposing Party at least thirty (30)
               days before the arbitration hearing, and that the preparer of
               each chart, graph, or summary is available for explanation and
               live cross-examination in person. Discovery disputes shall be
               decided by the arbitrator(s). The arbitrator(s) are empowered to
               issue subpoenas to compel compliance with requirements for pre-
               hearing exchange of witness lists and documents or deposition
               discovery, and to enforce the discovery rights and obligations of
               the Parties.

       16.3.4  Hearing. Unless otherwise agreed to by the Parties, the
               arbitration shall include the presentation of evidence and
               examination of witnesses at an oral hearing. The hearing shall be
               conducted to preserve its privacy and to allow reasonable
               procedural due process. Rules of evidence need not be strictly
               followed, and the hearing shall be streamlined. Documents shall
               be self-authenticating, subject to valid objection by the
               opposing Party. Expert reports, witness biographies, depositions,
               and affidavits may be utilized, subject to the opposing Party's
               right to a live cross-examination of the witness in person. The
               arbitrator(s) shall control the scheduling and conduct of the
               proceedings.

       16.3.5  Request for Relief. On the last day of the arbitration hearing,
               each Party shall submit to the arbitrator(s) and to each other a
               form of award, stating completely and in detail the relief sought
               in the arbitration, which may

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                                                                        Page 120
<PAGE>

               include an award of specific performance or injunctive relief
               (each a "Form of Award").

16.4   Arbitrator's Decision.

       16.4.1  The arbitrator(s) shall make their decision promptly and, unless
               otherwise mutually agreed to by the Parties in writing, no later
               than ten (10) days from the date of closing of the hearings or if
               oral hearings have been waived, from the date of transmitting the
               final statements and proofs to the arbitrator(s). The
               arbitrator's discretion to make their decision is limited to
               entering, without modification, the Form of Award submitted by
               one or the other Party. The award rendered by the arbitrator(s)
               shall be final, shall not constitute a basis for collateral
               estoppel as to any issue, and shall not be subject to vacation or
               modification except as provided under the Federal Arbitration
               Act. Judgment may be entered upon the award in a United States
               District Court of competent jurisdiction.

       16.4.2  Notwithstanding any other provision in this Agreement, if the
               Parties submit to arbitration any disputes concerning whether or
               not to incur any additional expenses for Additional Indications
               in excess of ****** dollars ($******) for the first Additional
               Indication, ****** dollars ($******) for the second Additional
               Indication (i.e., ****** dollars ($******) for both Additional
               Indications), the arbitrator(s) shall base his/her decision as to
               whether to spend such additional monies on whether any VP Product
               for such Additional Indications is commercially viable for both
               Parties, in accordance with each Party's own objective criteria
               for commercial viability, and not considering the commercial
               viability relative to other of the Party's products. In addition,
               in determining commercial viability, the arbitrator shall
               consider the probability of obtaining Regulatory Approval for
               such Additional Indication, and the anticipated date of obtaining
               Regulatory Approval, in light of the VP Exclusivity Period.
               Notwithstanding the foregoing in this Section 16.4.2, the
               arbitrator may not require the Parties to spend more than ******
               dollars ($******) for a single Additional Indication and ******
               dollars ($******) for both Additional Indications.

16.5   Costs.

       16.5.1  Generally. The Parties shall share equally the arbitrator(s) fees
               for the arbitration. Each Party shall be responsible for all
               costs and expenses such Party incurs in connection with
               arbitration.

       16.5.2  Exception for Bad Faith. Notwithstanding the foregoing, if the
               arbitrator(s) determine that one of the Parties did not proceed
               in good faith with respect to the matters submitted for
               arbitration, that Party shall bear fully both Party's expenses of
               arbitration.

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                                                                        Page 121
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     16.6  Governing Law of Arbitration. This arbitration provision shall be
           governed by, and all rights and obligations specifically enforceable
           under and pursuant to, the Federal Arbitration Act. Enforcement shall
           be sought only in a United States District Court of competent
           jurisdiction.

     16.7  Consolidation. No arbitration shall include, by consolidation,
           joinder, or in any other manner, any additional person not a Party to
           this Agreement, except by written consent of both Parties containing
           a specific reference to this Agreement. No counterclaims may be
           brought in the arbitration, unless those claims were the subject of
           the Parties' dispute resolution procedure set forth in Sections 3.10.

     16.8  Confidentiality. The substance and result of arbitration hereunder,
           and any materials disclosed in arbitration hereunder, shall be deemed
           Confidential Information within the meaning of Section 1.24.

17.  MISCELLANEOUS.

     17.1  Relationship of the Parties. Each Party shall bear its own costs
           incurred in the performance of its obligations hereunder without
           charge or expense to the other except as expressly provided in this
           Agreement. Neither Party shall have any responsibility for the
           hiring, termination or compensation of the other Party's employees or
           for any employee benefits of such employee. No employee or
           representative of a Party shall have any authority to bind or
           obligate the other Party to this Agreement for any sum or in any
           manner whatsoever, or to create or impose any contractual or other
           liability on the other Party without said Party's approval. Both
           Parties are independent contractors under this Agreement. Nothing
           herein contained shall be deemed to create an employment, agency,
           joint venture or partnership relationship between the Parties hereto
           or any of their agents or employees, or any other legal arrangement
           that would impose liability upon one Party for the act or failure to
           act of the other Party.

     17.2  No Solicitation. During the Term of this Agreement and for the two
           (2) years thereafter, a Party may not actively solicit an employee of
           the other Party to leave the employment of the other Party and accept
           employment with the first Party. Active solicitation shall not be
           deemed to include general advertisement not directed specifically to
           any employee or class of employees of the other Party.

     17.3  Further Actions. Each Party agrees to execute, acknowledge and
           deliver such further instruments, and to do all such other acts, as
           may be necessary or appropriate in order to carry out the purposes
           and intent of the Agreement.

     17.4  Force Majeure. The occurrence of an event which materially interferes
           with the ability of a Party to perform its obligations or duties
           hereunder which is not within the reasonable control of the Party
           affected, not due to malfeasance, and which could not with the
           exercise of due diligence have been avoided ("Force Majeure"),
           including, but not limited to, fire, accident, labor difficulty,
           strike, riot, civil commotion, act of God, shall not excuse such
           Party from the performance of

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                                                                        Page 122
<PAGE>

           its obligations or duties under this Agreement, but shall merely
           suspend such performance during the continuation of Force Majeure.
           The Party prevented from performing its obligations or duties because
           of Force Majeure shall promptly notify the other Party hereto (the
           "Notified Party") of the occurrence and particulars of such Force
           Majeure and shall provide the Notified Party, from time to time, with
           its best estimate of the duration of such Force Majeure and with
           notice of the termination thereof. The Party so affected shall use
           reasonable efforts to avoid or remove such causes of nonperformance,
           provided, however, that a Party shall not be required to settle any
           labor dispute or disturbance. Upon termination of Force Majeure, the
           performance of any suspended obligation or duty shall promptly
           recommence. Neither Party shall be liable to a Notified Party for any
           direct, indirect, consequential, incidental, special, punitive,
           exemplary or other damages arising out of or relating to the
           suspension or termination of any of its obligations or duties under
           this Agreement by reason of the occurrence of Force Majeure.

     17.5  Specific Performance. Each of the Parties acknowledges and agrees
           that the other Party will be damaged irreparably if any of the
           provisions of Sections 2.6, 2.7, 6.2.6, 10.1, 10.2, the first
           sentence of Section 10.5, Article 11, and 12 of this Agreement are
           not performed in all material respects or otherwise are breached.
           Accordingly and notwithstanding anything herein to the contrary, each
           of the Parties agrees that the other Party shall be entitled to an
           injunction or injunctions to prevent breaches of the provisions of
           Sections 2.6, 2.7, 6.2.6, 10.1, 10.2, the first sentence of Section
           10.5, Article 11, and 12of this Agreement and to enforce specifically
           such provisions of this Agreement and the terms and provisions
           thereof in any action instituted in any court or tribunal having
           jurisdiction over the Parties and the matter in addition to any other
           remedy to which it may be entitled, at law or in equity.

     17.6  Governing Law. This Agreement shall be governed by and construed in
           accordance with the law of the Commonwealth of Pennsylvania, without
           regard to the conflict of law principles of Pennsylvania or any other
           jurisdictions. Each Party hereby irrevocably and unconditionally
           submits for itself and its property in any legal action or proceeding
           relating to or arising out of this Agreement, or any of the
           transactions contemplated hereby, to the non-exclusive general
           jurisdiction of the Courts of the Commonwealth of Pennsylvania, the
           courts of the United States of America for the Eastern District of
           Pennsylvania, and appellate courts from any thereof, and agrees that
           any such action or proceeding shall be brought only in such courts.

     17.7  Assignment. Neither Party may assign or transfer this Agreement or
           any righs or obligations hereunder without the prior written consent
           of the other Party, except that a Party may make such an assignment
           without the other Party's consent to Affiliates, however, and such
           assignment to an Affiliate shall not relieve such Party of its
           obligations under this Agreement to the extent not performed by such
           Affiliate, or to a successor to all or substantially all of the
           related business assets of such Party relating to this Agreement,
           whether by way of a merger, sale of

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                                                                        Page 123
<PAGE>

           stock, sale of assets or other similar transaction. Notwithstanding
           the foregoing, in no event shall either Party have the right or power
           to assign this Agreement or any rights or obligations hereunder to
           any Person that is not domiciled in the United States.

     17.8  Notices. All demands, notices, consents, approvals, reports, requests
           and other communications hereunder must be in writing and will be
           deemed to have been duly given only if delivered personally or by
           facsimile transmission or by mail (first class, postage prepaid) to
           the Parties at the following addresses or facsimile numbers:

           If to ViroPharma:  ViroPharma Incorporated
                              405 Eagleview Boulevard
                              Exton, PA 19341
                              Facsimile No.: 610-458-7380
                              Attention: Vice President, Commercial Operations

                         with a copy to: Vice President and General Counsel

           If to Aventis:     Aventis Pharmaceuticals Inc.
                              Route 202-206
                              P.O. Box 6800
                              Bridgewater, NJ 08807, U.S.A.
                              Facsimile: 1-908-231-4480
                              Attention: Vice President, Legal Department

           or to such other address as the addressee shall have last furnished
           in writing to the addressor in accord with this provision.

     17.9  Severability.

           17.9.1  If any provision of this Agreement is held to be illegal,
                   invalid or unenforceable under any applicable present or
                   future Law, and if the rights or obligations of either Party
                   hereto under this Agreement will not be materially and
                   adversely affected thereby, (a) such provision will be fully
                   severable, (b) this Agreement will be construed and enforced
                   as if such illegal, invalid or unenforceable provision had
                   never comprised a part hereof, (c) the remaining provisions
                   of this Agreement will remain in full force and effect and
                   will not be affected by the illegal, invalid or unenforceable
                   provision or by its severance herefrom, and (d) in lieu of
                   such illegal, invalid or unenforceable provision, there will
                   be added automatically as a part of this Agreement, a legal,
                   valid and enforceable provision as similar in terms to such
                   illegal, invalid or unenforceable provision as may be
                   possible.

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                                                                        Page 124
<PAGE>

            17.9.2  If any right or obligation of either Party under this
                    Agreement contravenes any provision of the SaSy Agreement (a
                    "Conflicting Obligation"), the Parties shall consult and
                    agree in good faith to amend this Agreement in a
                    commercially reasonable manner so that such right or
                    obligation no longer contravenes the SaSy Agreement. Neither
                    Party shall seek damages resulting from the breach of a
                    Conflicting Obligation other than, (a) damages which were
                    incurred before the date on which one Party has given notice
                    to the other Party that such Conflicting Obligation
                    conflicts with the SaSy Agreement, or (b) thereafter,
                    damages which such other Party could not reasonably have
                    avoided.

     17.10  Headings. The descriptive headings of this Agreement are for
            convenience only, and shall be of no force or effect in construing
            or interpreting any of the provisions of this Agreement.

     17.11  Waiver and Remedies. Any term or condition of this Agreement may be
            waived at any time by the Party that is entitled to the benefit
            thereof, but no such waiver shall be effective unless set forth in a
            written instrument duly executed by or on behalf of the Party or
            Parties waiving such term or condition. No waiver by any Party of
            any term or condition of this Agreement, in any one or more
            instances, shall be deemed to be or construed as a waiver of the
            same or any other term or condition of this Agreement on any future
            occasion. All remedies, either under this Agreement or by law or
            otherwise afforded, will be cumulative and not alternative.

     17.12  Entire Agreement. This Agreement and the Stock Purchase Agreement
            between the Parties dated the date hereof constitute the entire
            agreement between the Parties hereto with respect to the within
            subject matter and supersede all previous agreements, whether
            written or oral, except that the Standstill Agreement shall remain
            in full force and effect, except as expressly provided in Section
            12.2.

     17.13  Amendment. This Agreement may be altered, amended or changed only by
            a writing making specific reference to this Agreement and signed by
            duly authorized representatives of ViroPharma and Aventis.

     17.14  No Implied License. Nothing in this Agreement shall be deemed to
            constitute the grant of any license or other right in either Party
            to or in respect of any product, patent, trademark, Confidential
            Information, trade secret or other data or any other intellectual
            property of the other Party except as expressly set forth herein.

     17.15  Third Party Beneficiaries. None of the provisions of this Agreement
            shall be for the benefit of or enforceable by any Third Party,
            except for the Aventis Indemnitees and the ViroPharma Indemnitees to
            the extent expressly provided in Article 15, including, without
            limitation, any creditor of either Party hereto. No such Third Party
            shall obtain any right under any provision of this Agreement or

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                                                                        Page 125
<PAGE>

            shall by reasons of any such provision make any claim in respect of
            any debt, liability or obligation (or otherwise) against either
            Party hereto.

     17.16  Wording. Unless the context of this Agreement otherwise requires,
            (a) words of either gender include each other gender; (b) words
            using the singular or plural number also include the plural or
            singular number, respectively; (c) the terms "hereof," "herein,"
            "hereby," and derivative or similar words refer to this entire
            Agreement; and (d) the terms "Article" and "Section" refer to the
            specified Article and Section of this Agreement. Whenever this
            Agreement refers to a number of days, unless otherwise specified,
            such number shall refer to calendar days.

     17.17  Representation by Legal Counsel. Each Party hereto represents that
            it has been represented by legal counsel in connection with this
            Agreement and acknowledges that it has participated in the drafting
            hereof. In interpreting and applying the terms and provisions of
            this Agreement, the Parties agree that no presumption shall exist or
            be implied against the Party that drafted such terms and provisions.

     17.18  Debarment. Each Party agrees that it will not use, in any capacity,
            in connection with any of its obligations to be performed under this
            Agreement any individual who has been debarred under the FD&C Act or
            the Generic Drug Enforcement Act.

     17.19  Counterparts. This Agreement may be executed in any number of
            counterparts, each of which, when executed, shall be deemed to be an
            original and all of which together shall constitute one and the same
            agreement.

IN WITNESS WHEREOF, ViroPharma and Aventis, by their duly authorized officers,
have executed this Agreement as of the date first written above.

VIROPHARMA INCORPORATED                       AVENTIS PHARMACEUTICALS, INC.

By: /s/ Michel de Rosen                       By: /s/ Jerry Belle
    -------------------                           ---------------
   Michel de Rosen                                Jerry Belle
   President and Chief Executive Officer          President and Chief Executive
                                                  Officer

________________________________________________________________________________
                                                                        Page 126
<PAGE>

                                  Exhibit 1.9
                                 Aventis Logo

________________________________________________________________________________
                                                                          Page 1
<PAGE>

                                 Exhibit 1.12
                             Aventis Trade Policy

                            AVENTIS PHARMACEUTICALS

                                TRADE POLICIES
                         Policy Effective July 1, 2000

________________________________________________________________________________
                                                                          Page 2
<PAGE>

                           TRADE POLICIES - AVENTIS

________________________________________________________________________________
                                                                          Page 3
<PAGE>

Trade Sales Policy
We will sell direct to franchised warehousing customers who meet the provisions
listed within our Franchised Trade Agreement, including the key criteria listed
below:

 . Have the capability to place orders electronically

 . Meet minimum order requirements

 . Meet credit requirements

We will also sell to those tax-supported entities who are precluded by
law/policy/procedure from purchasing from any source other than the original
manufacturer (i.e., city/county/state hospitals, prisons, universities, health
centers, etc.) and hospitals with specific purchasing needs.

For products that have special distribution requirements, Aventis maintains the
right to establish separate criteria for direct status.

Terms
-----
2%   30 days, date of invoice
NET  31 days, date of invoice

EFT Terms:

2%   34 days, date of invoice
NET  35 days, date of invoice

Pricing
-------
All direct prices will be at NET LIST PRICE, as listed in our current price
list. We will also include our MANUFACTURER'S SUGGESTED PRICE in our sales
catalog.

Minimum Order Requirements
--------------------------
The minimum order acceptable for shipment is $10,000 NET. Products must be
ordered in unit packs as listed on our current price list. All orders not
meeting the dollar minimum and/or not meeting the unit pack multiples will not
be processed. The only exceptions to this policy will be initial orders for new
product introductions and products with special distribution needs (i.e.,
refrigerated products, etc.).

Drop Shipment Policy
--------------------
Orders that meet minimum order requirements of $10,000 NET can be drop-shipped
to approved accounts.

________________________________________________________________________________
                                                                          Page 1
<PAGE>

Return Goods Policy and Procedures
----------------------------------
Aventis will provide credit for all product returns that meet the following
criteria:

Returns Criteria

Returnable Products:
--------------------
 . Product returned within 6 months of expiration
 . Product returned that is no more than 12 months past expiration
 . Product returned in the original container
 . Product returns valued at more than $25,000 require preauthorization
 . Partials except for liquids, lotions, ampules, syringes or gels

Damaged or shortage claims must be filed within 15 days of customer's receipts
of product.

Non- returnable Products:
------------------------
 . Products returned more than 1 full year past expiration date
 . Products damaged by fire and/or water
 . Repackaged products
 . Professional samples
 . Distressed merchandise obtained through a bankruptcy or sacrifice sale, a
   going-out-of-business sale, or other merchandise considered under the
   classification of "distressed merchandise"
 . Merchandise obtained illegally or via diverted means; this includes products
   being imported from countries outside the United States
 . Partial liquids, lotions, ampules, syringes or gels

Controlled Substances
---------------------
Controlled substances should be packaged separately from other returns.

Miscellaneous
-------------
Customers should return product to the Aventis designated third-party return
goods processor. Call the Aventis Customer Service Department with any
questions.

 . Freight should be prepaid by customer
 . Reimbursement
  .  Direct customers will be reimbursed via credit memo
  .  Direct customers will receive credit through their wholesaler
  .  Non-direct accounts that return product directly to the Aventis designated
     third-party return goods processor will be reimbursed via check
  .  All returns will be credited at current NET LIST PRICE unless purchased at
     a contract price, with credit being given at the contract price
  .  Qualified partials will be credited for the exact count returned

________________________________________________________________________________
                                                                          Page 2
<PAGE>

Aventis reserves the right, prior to credit or refund, to verify the original
purchase documents as proof that the product being returned has been through the
normal distribution channels of Aventis and to determine purchase price. Aventis
also reserves the right to destroy ineligible items with no credits.

Freight Charges
---------------
Postage or shipping charges will be prepaid and FOB destination on all orders
where routing is done by Aventis. If special routing is requested by the direct
account, the entire freight and handling charge will be billed to the customer.
All drop shipments will be prepaid.

Natural Disaster Policy -
-------------------------
Retail Outlets
--------------
Aventis will support a natural disaster policy for retail outlets. The criteria
is as follows:

 . Aventis will expedite a disaster protection pack in the event of natural
   disaster (fire, flood, hurricane, tornado, etc.)
 . Aventis will replace the loss on a unit-per-unit basis
 . Documentation of disaster must be obtained prior to shipment (newspaper
   clipping, fire inspection report or similar documentation)
 . Aventis will only cover noninsured products

This policy does not apply to warehouses.

New Warehouse Dating Policy
---------------------------
Aventis will provide our direct customers 30 additional days' dating (maximum 2%
60days, date of invoice, NET 61) on their initial order when opening a new
distribution facility.

 . Policy does not provide for expansion or consolidation of existing
   facilities
 . Policy does not provide for new business shipped through existing
   facilities
 . Authorization must be obtained through Aventis

Exception
---------
Aventis reserves the right to make exceptions to this policy due to business
needs.

________________________________________________________________________________
                                                                          Page 3
<PAGE>

                                 Exhibit 1.61
           Sample Calculation of Net Sales of a Combination Product

Background:
----------

Jurgenex(TM) is a combination product containing 20 mg of Compound V (a VP
Compound) and 25 mg of Compound A (a non-VP Compound).  In Calendar Year 0, Net
Sales of Jurgenex were $100,000,000.

Compound V is sold in three different formulations which were sold at the
following volumes and prices in Calendar Year 0:

<TABLE>
<CAPTION>
                   Mg Compound V       Number of Retail
Formulation        per Retail Unit     Units Sold         Price per Retail Unit
-----------        ---------------     ----------------   ---------------------
<S>                <C>                 <C>                <C>
Formulation A      100 mg              50,000             $125
                   100 mg              55,000             $115
                   100 mg              70,000             $112

Formulation B      80 mg               45,000             $110
                   80 mg               48,000             $108

Formulation C      65 mg               10,000             $180
</TABLE>

Compound A is sold in a single formulation containing 150 mg per retail unit,
which sold for $60 per retail unit in a volume of 100,000 retail units in
Calendar Year 0.

For purposes of this example, the price per retail unit will be assumed to be
the gross invoiced sales price to Third Parties other than contractors of a
Party, less the deductions described in Sections 1.61.1-6.

Calculation:
-----------

Compound V: The weighted average price per mg of Compound V in product
containing Compound V only is:

     ((($125/100mg) x 50,000 units) + (($115/100mg) x 55,000 units) +
     (($112/100mg) x 70,000 units) + (($110/80mg) x 45,000 units) + (($108/80mg)
     x 48,000 units) + (($180/65mg) x 10,000 units)) / (50,000 units + 55,000
     units + 70,000 units + 45,000 units + 48,000 units + 10,000 units) =
     $1.29/mg.

Compound A: The weighted (and unweighted) average price per mg of Compound A in
product containing Compound A only is: ((($60/150mg) x 100,000 units)) / 100,000
units = $0.40/mg.

Net Sales of Compound V in Jurgenex(TM): The Net Sales of Compound V in
Jurgenex(TM) is the Net Sales of Jurgenex(TM) multiplied by AX/(AX +BY), where A
is the weighted average price per
________________________________________________________________________________
                                                                          Page 1
<PAGE>

mg of Compound V, X is the number of mg of Compound V in Jurgenex(TM), B is the
weighted average price per mg of Compound A, and Y is the number of mg of
Compound a in Jurgenex(TM), or:

     $100,000,000 x ($1.29/mg x 20mg) / (($1.29/mg x 20mg) + ($0.40/mg x 25mg))
     = $72,067,039.11.

________________________________________________________________________________
                                                                          Page 2
<PAGE>

                                 Exhibit 1.81
                                 SaSy Patents

<TABLE>
<CAPTION>

                    PATENT        FILING        GRANT
COUNTRY             (Application) DATE          DATE          STATUS
---------------------------------------------------------------------------
<S>                 <C>           <C>           <C>           <C>

U.S.                5,175,177     07/17/91      12/29/92      in force
U.S.                5,643,929     05/19/95      07/01/97      in force
U.S.                5,175,178     06/04/90      12/29/92      in force
U.S.                5,567,719     06/07/95      10/22/96      in force
U.S.                5,650,419     08/30/96      07/22/97      in force
U.S.                5,821,257     03/31/98      10/13/98      in force
U.S.                4,857,539     06/16/87      08/15/89      in force
U.S.                5,110,821     06/07/90      05/05/92      in force
U.S.                5,514,679     05/13/94      05/07/96      in force
U.S.                5,464,848*    10/01/93      11/07/95      in force
U.S.                5,453,433*    05/13/94      09/26/95      in force
</TABLE>
     *  Patents for which SaSy has primary responsibility.

________________________________________________________________________________
                                                                          Page 1
<PAGE>

                                 Exhibit 1.94
                                  Trademarks

<TABLE>
<CAPTION>
Mark            Country          Trademark No.        Filing Date    Registration      Status
                                 (Application No.)                   Date
------------------------------------------------------------------------------------------------------
<S>             <C>              <C>                  <C>            <C>               <C>
NUVIX           U.S.A.           (75/597,640)         12/02/98       N/A               Pending
----------------------------------------------------------------------------------------------------
PICOVIR         U.S.A.           (75/597,699)         12/02/98       N/A               Pending
----------------------------------------------------------------------------------------------------
VIRNAX          U.S.A.           (75/597,698)         12/02/98       N/A               Pending
----------------------------------------------------------------------------------------------------
</TABLE>

________________________________________________________________________________
                                                                          Page 1
<PAGE>

                                 Exhibit 1.99
                                ViroPharma Logo

                                    [LOGO]

________________________________________________________________________________
                                                                          Page 1
<PAGE>

                                 Exhibit 1.100
                              ViroPharma Patents

<TABLE>
<CAPTION>

           PATENT                  FILING     GRANT
COUNTRY    APPLICATION             DATE       DATE       STATUS
--------------------------------------------------------------------
<S>        <C>                     <C>        <C>        <C>
******     ******                  ******     ******     ******

******     ******                  ******     ******     ******

******     ******                  ******     ******     ******

--------------------------------------------------------------------
</TABLE>
     ******

________________________________________________________________________________
                                                                          Page 1
<PAGE>

                                 Exhibit 4.4.1
                      Initial Development Plan and Budget

                                  Picovir(TM)

                               Development Plan
<PAGE>

                               Exhibit 6.4.7(a)
                           Initial Product Suppliers

1.   API Manufacturers

F.I.S. (Fabbrica Italiano Sintetici)
Viale Milano
36041 Alpe di Montecchio Maggiore
Vincenza, Italy

PCAS (Produits Chemiques Auxilliares et de Synthese)
19 Route de Meulan
78520 Limay, France

2.   Micronizer

Micron Technologies, Inc.
435 Creamery Way
Exton, PA  19341
USA

3.   Finished Product Manufacturer

Patheon, Incorporated
2100 Syntex Court
Mississauga, Ontario LSN 7K9
Canada

________________________________________________________________________________
                                                                          Page 1
<PAGE>

                                  Exhibit 8.2
           STOCK PURCHASE AGREEMENT--Form of Agreement to be Signed

     THIS STOCK PURCHASE AGREEMENT (this "Agreement") is made as of September 9,
2001, by and between ViroPharma Incorporated ("ViroPharma"), a Delaware
corporation with its principal place of business at 405 Eagleview Boulevard,
Exton, PA 19341, and Aventis Pharma Inc., a Canadian corporation with its
principal place of business at 2150 Saint Elzear Boulevard West, Laval, Quebec,
Canada, H7L 4A8 ("Aventis").

                                   RECITALS
                                   --------

     WHEREAS, ViroPharma and an Affiliate of Aventis have entered into that
certain Copromotion and Codevelopment Agreement dated September 9, 2001 (the
"Copromotion and Codevelopment Agreement"); and

     WHEREAS, in connection with the execution of the Copromotion and
Codevelopment Agreement, ViroPharma desires to sell to Aventis and Aventis
desires to purchase from ViroPharma shares of common stock of ViroPharma on the
terms and subject to the conditions set forth in this Agreement.

     NOW, THEREFORE, in consideration of the foregoing recitals and the mutual
covenants and agreements contained herein, the Parties hereto, intending to be
legally bound, do hereby agree as follows:

1.   Definitions.  The capitalized terms used herein shall have the meanings
     -----------
ascribed to them below, provided that capitalized terms used herein that are not
defined herein shall have the meanings ascribed to them in the Copromotion and
Codevelopment Agreement:

     1.1  "Affiliate" means any person or entity that directly or indirectly
           ---------
controls or is controlled by or is under common control with ViroPharma or
Aventis, as the case may be, but only for so long as said control shall
continue. As used herein the term "control" means the direct or indirect
ownership of over fifty percent (50%) of the outstanding voting securities of an
entity, or the right to receive over fifty percent (50%) of the profits or
earnings of an entity (or, in either case, such lesser percentage which is the
maximum allowed to be owned by a foreign corporation in a particular
jurisdiction). Such other relationship as in fact gives such individual or
entity the power or ability to control the management, business and affairs of
an entity shall also be deemed to constitute control.

     1.2  "Closing" has the meaning ascribed to it in Section 3.1 hereof.
           -------

     1.3  "Closing Date" means the day on which the transaction that is the
           ------------
subject of such Closing is consummated.

     1.4  "Common Stock" means the common stock of ViroPharma, par value $0.002
           ------------
per share.

________________________________________________________________________________
                                                                          Page 1
<PAGE>

     1.5   "Deemed Market Price" has the meaning ascribed to it in Section 2
            -------------------
hereof.

     1.6   "Exchange Act" means the Securities Exchange Act of 1934, as amended,
            ------------
together with the rules and regulations promulgated thereunder.

     1.7   "Excluded Registration Statements" means (a) Registration Statements
            --------------------------------
on Form S-8 (or any successor or similar form) relating to employee benefit
plans, (b) Registration Statements on Form S-4 (or any successor or similar
form) relating to corporate reorganizations or other transactions under Rule 145
of the Securities Act, or (c) Registration Statements covering shares of
ViroPharma's capital stock issued pursuant to that certain Investment Agreement
(the "Perseus Shares") dated May 5, 1999 between ViroPharma and PSV, LP
(previously known as Perseus-Soros BioPharmaceutical Fund, LP) (the "Perseus
Agreement"), and any Common Stock issued upon conversion of the Perseus Shares
or upon exercise of warrants issued pursuant to the Perseus Agreement.

     1.8   "GAAP" means generally accepted accounting principles in the United
            ----
States.

     1.9   "Holder" means each person owning of record Registrable Securities
            ------
that have not been sold to the public.

     1.10  "Intellectual Property" means trademarks, trade names, trade dress,
            ---------------------
service marks, copyrights, and similar rights (including registrations and
applications to register or renew the registration of any of the foregoing),
patents and patent applications, trade secrets, and any other similar
intellectual property rights.

     1.11  "Intellectual Property License" means any license, permit,
            -----------------------------
authorization, approval, contract or consent granted, issued by or with any
Person relating to the use of Intellectual Property.

     1.12  "Knowledge" means the knowledge of such party, assuming that such
            ---------
party engaged in reasonable inquiry or investigation with respect to the
relative subject matter.

     1.13  "Material Adverse Effect" on or with respect to an entity (or group
            -----------------------
of entities taken as a whole) means any state of facts, event, change or effect
that has had, or that might be reasonably expected to have, a material adverse
effect on the business, properties, results of operations or financial condition
of such entity (or of such group of entities taken as a whole).

     1.14  "Nasdaq" means the Nasdaq Stock Market, Inc.
            ------

     1.15  "Party" means a party to this Agreement.
            -----

     1.16  "Purchase Price" has the meaning ascribed to it in Section 2.1.
            --------------

     1.17  "Person" means any individual, firm, corporation, partnership,
            ------
limited liability company, trust, incorporated or unincorporated association,
joint venture, joint stock company,

________________________________________________________________________________
                                                                          Page 2
<PAGE>

government (or an agency or political subdivision thereof) or other entity of
any kind, and shall include any successor (by merger or otherwise) of such
entity.

     1.18  "Register," "Registered," and "Registration" refer to a registration
            --------    ----------        ------------
effected by preparing and filing a Registration Statement in compliance with the
Securities Act, and the declaration or ordering of effectiveness of such
Registration Statement or document by the SEC.

     1.19  "Registrable Securities" means (a) the Shares; and (b) any shares of
            ----------------------
Common Stock of ViroPharma or other securities issued as (or issuable upon the
conversion or exercise of any warrant, right or other security which is issued
as) a dividend or other distribution with respect to, or in exchange for or in
replacement of, the Shares by way of stock dividend, stock split or in
connection with a combination of shares, recapitalization or other
reorganization or otherwise. Notwithstanding the foregoing, as to any particular
Shares or other securities described above, once issued they shall cease to be
Registrable Securities when (x) a registration statement with respect to the
sale of such securities shall have become effective under the Securities Act and
such securities shall have been disposed of in accordance with such registration
statement, (y) they shall have been distributed pursuant to Rule 144 (or any
successor provision) under the Securities Act, or (z) they shall have been
otherwise transferred in a private transaction in which the rights under this
Section 7 hereof have not been assigned.

     1.20  "Registration Expenses" means all expenses incurred by ViroPharma in
            ---------------------
complying with Section 7.1 hereof, including, without limitation, registration
and filing fees, printing and reproduction expenses, fees and disbursement of
counsel for ViroPharma, blue sky fees and expenses, messenger and delivery
expenses, the expenses of any special audits or "comfort letters" incident to or
required by any such registration and any fees and disbursements of underwriters
customarily paid by issuers or seller of securities, but excluding Selling
Expenses.

     1.21  "Registration Statement" means a Registration Statement filed
            ----------------------
pursuant to the Securities Act.

     1.22  "Rights Agreement" means that certain Rights Agreement dated
            ----------------
September 10, 1998 between ViroPharma and StockTrans, Inc.

     1.23  "SEC Documents" means ViroPharma's Form S-3 filed with the SEC on
            -------------
July 3, 2001, its Annual Report on Form 10-K for the year ended December 31,
2000, its Quarterly Reports on Form 10-Q for the quarters ended June 30, 2001
and March 31, 2001, and its Proxy Statement for its Annual Meeting of
Stockholders held on June 11, 2001, each as filed with the SEC, but shall not
include any portion of any document which is not deemed to be filed under
applicable SEC rules and regulations.

     1.24  "SEC" means the U.S. Securities and Exchange Commission.
            ---

     1.25  "Securities Act" means the Securities Act of 1933, as amended,
            --------------
together with the rules and regulations promulgated thereunder.

________________________________________________________________________________
                                                                          Page 3
<PAGE>

     1.26  "Selling Expenses" shall mean all underwriting discounts and selling
            ----------------
commissions applicable to the sale, and all fees and expenses of counsel
exclusively for Aventis, if any.

     1.27  "Shares" means the shares of Common Stock to be acquired by Aventis
            ------
hereunder.

     1.28  "Transaction Documents" means this Agreement, the Copromotion and
            ---------------------
Codevelopment Agreement, and any other agreement or instrument executed by
ViroPharma in connection with the foregoing.

     1.29  "Triggering Event" means Regulatory Approval of an NDA in the United
            ----------------
States for a VP Product for the First Indication.

     1.30  "Voting Stock" means securities of any class or series of a
            ------------
corporation or association the holders of which are ordinarily, in the absence
of contingencies, entitled to vote generally in matters put before the
shareholders or members of such corporation or association, or securities
convertible or exchangeable into or exercisable for any such securities.

2.   Purchase and Sale.
     -----------------

     2.1   Subject to Section 2.2 below, at the Closing, ViroPharma will sell to
Aventis and Aventis will purchase from ViroPharma, for the aggregate
consideration of $20,000,000, as may be adjusted in Section 2.2 below (the
"Purchase Price"), a number of shares of Common Stock equal to the quotient of
$20,000,000 divided by the Deemed Market Price. For the purposes of this Section
2, the "Deemed Market Price" shall be equal to the average of the closing sales
prices of ViroPharma's Common Stock, as reported by Nasdaq, for those days on
which ViroPharma's Common Stock was traded during the twenty (20) trading days
ending on the trading day immediately preceding the date of the Triggering
Event; provided, however, that if ViroPharma takes the steps contemplated under
Section 9.1(c)(iii), then the Deemed Market Price shall be equal to the average
of the closing sales prices of ViroPharma's Common Stock as reported by Nasdaq
for those days on which ViroPharma's Common Stock was traded during the twenty
(20) trading days immediately following the date that ViroPharma again becomes
listed for trading as contemplated by Section 9.1(c)(iii).

     2.2   (a)  Notwithstanding the foregoing, the number of shares purchasable
hereunder shall not be in excess of nineteen and nine tenths percent (19.9%) of
the number of shares of Common Stock issued and outstanding on the date hereof,
which number shall be subject to appropriate and equitable adjustment for any
stock split, stock dividend or reclassification of the Common Stock or similar
event (the "Maximum Number of Shares"). Only shares of Common Stock acquired
pursuant to this Agreement will be included in determining whether the
limitation contained herein would be exceeded for purposes of this Section.

           (b)  In the event the number of shares to be acquired pursuant to
Section 2.1 would exceed the Maximum Number of Shares, then notwithstanding
anything to the contrary in

________________________________________________________________________________
                                                                          Page 4
<PAGE>

Section 2.1, at the Closing ViroPharma will sell to Aventis and Aventis will
purchase from ViroPharma the Maximum Number of Shares for an aggregate
consideration equal to the product of the Maximum Number of Shares times the
Deemed Market Price.

3.   Closing.
     -------

     3.1   Closing. The completion of the sale and purchase of the Shares (the
           -------
"Closing") shall be held within five (5) business days after the satisfaction of
the closing conditions set forth in Article 6, or on such other date as the
parties shall mutually agree.

     3.2  Delivery.  At the Closing, subject to the terms and conditions hereof,
          --------
Aventis shall deliver to ViroPharma the Purchase Price by wire transfer to an
account designated in writing by ViroPharma no less than two (2) business days
prior to the Closing, and ViroPharma will deliver to Aventis a stock
certificate, in the name of Aventis, representing the Shares purchased at the
Closing, dated as of the Closing Date, against payment of such Purchase Price.

     3.3  Location.  The Closing shall occur at the offices ViroPharma, unless
          --------
otherwise agreed to by the Parties.

4.   Representations and Warranties of ViroPharma. ViroPharma hereby represents
     --------------------------------------------
and warrants to Aventis as of the date hereof and as of the Closing Date (except
as set forth below), as follows:

     4.1  Capitalization.    As of August 31, 2001, the authorized capital stock
          ---------------
of ViroPharma consisted of (a) 100,000,000 shares of Common Stock, of which (i)
18,699,695 shares were issued and outstanding, (ii) up to 690,000 shares have
been reserved for issuance upon exercise of outstanding common stock warrants,
(iii) 3,750,000 shares have been reserved for issuance under ViroPharma's Stock
Option and Restricted Share Plan, (iv) 300,000 shares have been reserved for
issuance under ViroPharma's Employee Stock Purchase Plan, and (v) 1,649,107
shares have been reserved for issuance upon exercise of outstanding six percent
(6%) convertible subordinated notes; and (b) 5,000,000 shares of preferred
stock, none of which is outstanding and 200,000 shares of which have been
designated the Series A Junior Participating Preferred Shares, par vale $.01 per
share, and have been reserved for issuance pursuant to the Rights Agreement. All
issued and outstanding shares of ViroPharma's capital stock have been duly
authorized and validly issued, and are fully paid and nonassessable. As of
August 31, 2001, except as referred to in Exhibit 4.1 attached hereto, there are
no preemptive or similar rights on the part of any holder of any class or
securities of ViroPharma. As of August 31, 2001, except as set forth in the SEC
Documents, as set forth on Exhibit 4.1 attached hereto or as described or
referred to above, there are no securities convertible into or exchangeable for,
or options, warrants, calls subscriptions, rights, contracts or understandings
of any kind to which ViroPharma is a party or by which it is bound obligating
ViroPharma to issue, deliver or sell, or cause to be issued, delivered or sold
additional shares of its capital stock. As of August 31, 2001, except for the
repurchase of shares owned by employees upon termination of employment, there
are no outstanding agreement of ViroPharma to repurchase, redeem or otherwise
acquire any shares of its capital stock. As of August 31, 2001, ViroPharma does
not have any subsidiaries or any equity interest with a value of $250,000 or
more in any corporation or entity.

________________________________________________________________________________
                                                                          Page 5
<PAGE>

     4.2   Litigation.  There is no action, suit, proceeding nor, to its
           ----------
Knowledge, any investigation, pending or currently threatened against ViroPharma
that questions the validity of this Agreement or the issuance of the Common
Stock contemplated hereby, nor to its Knowledge, is there any basis therefor. As
of August 31, 2001, there is no other action, suit, or proceeding pending or, to
the Knowledge of ViroPharma, currently threatened against ViroPharma that might,
individually or in the aggregate, result in Material Adverse Effect. As of
August 31, 2001, ViroPharma is not subject to any consents, orders, decrees or
judgments of any governmental entity that, individually or in the aggregate, may
have a Material Adverse Effect.

     4.3   Organization and Good Standing. ViroPharma is a corporation duly
           ------------------------------
organized, validly existing and in good standing under the laws of the State of
Delaware and has all requisite corporate power and authority to carry on its
business as now conducted. ViroPharma is duly qualified and is in good standing
as a foreign corporation in each jurisdiction in which the properties owned,
leased or operated, or the business conducted, by it requires such qualification
except where the failure to be so qualified or in good standing, individually or
in the aggregate, would not have a Material Adverse Effect.

     4.4   Authorization.  All corporate action on the part of ViroPharma, its
           -------------
officers, directors and stockholders necessary for the authorization, execution
and delivery of the Transaction Documents have been taken. ViroPharma has the
requisite corporate power to enter into the Transaction Documents and to carry
out and perform its obligations thereunder. The Transaction Documents have been
duly authorized, executed and delivered by ViroPharma and, upon due execution
and delivery by Aventis, each Transaction Document will be a valid and binding
agreement of ViroPharma, except as enforceability may be limited by bankruptcy,
insolvency, reorganization, moratorium or similar laws affecting creditors'
rights generally or by equitable principles.

     4.5   No Conflict With Other Instruments.  The execution, delivery and
           ----------------------------------
performance of the Transaction Documents will not result in any violation of, be
in conflict with, cause any acceleration or any increased payments under, or
constitute a default under, with or without the passage of time or the giving of
notice: (a) any provision of ViroPharma's Amended and Restated Certificate of
Incorporation or Bylaws as in effect on the date hereof or at the Closing; (b)
any provision of any judgment, decree or order to which ViroPharma is a party or
by which it is bound, or (c) any note, mortgage, material contract or agreement,
or any license, waiver, exemption, order or permit.

     4.6   Disclosure Documents.
           --------------------

           (a)  ViroPharma's SEC Documents: (i) complied in all material
respects with the applicable requirements of the Securities Act or Exchange Act,
as applicable, as such requirements were in effect on the date that such SEC
Document was filed with the SEC, and (ii) when filed with the SEC, did not
contain any untrue statement of material fact or omit to state any material fact
required to be stated therein or necessary in order to make the statements
therein, in light of the circumstances under which they were made, not
misleading.

________________________________________________________________________________
                                                                          Page 6
<PAGE>

           (b)  The audited financial statements of ViroPharma included in
ViroPharma's SEC Documents comply in all material respects with the published
rules and regulations of the SEC with respect thereto, and such audited
financial statements (i) were prepared from the books and records of ViroPharma,
(ii) were prepared in accordance with GAAP applied on a consistent basis (except
as may be indicated therein or in the notes or schedules thereto) and (iii)
present fairly the financial position of ViroPharma as of the dates thereof and
the results of operations and cash flows for the periods then ended. The
unaudited financial statements included in the SEC Documents comply in all
material respects with the published rules and regulations of the SEC with
respect thereto, and such unaudited financial statements (i) were prepared from
the books and records of ViroPharma, (ii) were prepared in accordance with GAAP,
except as otherwise permitted under the Exchange Act and the rules and
regulations thereunder, on a consistent basis (except as may be indicated
therein or in the notes or schedules thereto) and (iii) present fairly the
financial position of ViroPharma as of the dates thereof and the results of
operations and cash flows (or changes in financial condition) for the periods
then ended, subject to normal year-end adjustments and any other adjustments
described therein or in the notes or schedules thereto

     4.7   Absence of Certain Events and Changes.  During the period commencing
           -------------------------------------
on December 31, 2000 and continuing through August 31, 2001, ViroPharma has
conducted its business in the ordinary course consistent with past practice and
there has not been any event, change or development which, individually or in
the aggregate, would have a Material Adverse Effect, taken as a whole.

      4.8  Compliance with Applicable Law.  As of August 31, 2001, ViroPharma is
           ------------------------------
in compliance in all material respects with all material statutes, laws,
regulations, rules, judgments, orders and decrees of all governmental entities
applicable to it that relate to its business, and ViroPharma has not received
any notice alleging noncompliance except, with reference to all the foregoing,
where the failure to be in compliance would not, individually or in the
aggregate, have a Material Adverse Effect taken as a whole.

      4.9  Valid Issuance Of Shares.  When issued, sold and delivered in
           ------------------------
accordance with the terms hereof for the consideration expressed herein, the
Shares will be duly and validly authorized and issued, fully paid and
nonassessable and, based in part upon the representations of Aventis in Section
6.3 of this Agreement, will be issued in compliance with all applicable federal
and state securities laws.

     4.10  Governmental Consents.  No consent, approval, order or authorization
           ---------------------
of, or registration, qualification, designation, declaration or filing with, any
federal, state or local governmental authority on the part of ViroPharma is
required in connection with the consummation of the transactions contemplated by
the Transaction Documents, except for notices required or permitted to be filed
with certain state and federal securities commissions, which notices will be
filed on a timely basis.

     4.11  No Brokers.  Other than Lazard Freres & Co. LLC which will be the
           ----------
sole obligation of ViroPharma, no broker, finder or investment banker is
entitled to any brokerage,

________________________________________________________________________________
                                                                          Page 7
<PAGE>

finder's or other fee or commission in connection with the transactions
contemplated by this Agreement based on arrangements made by ViroPharma.

     4.12  Delaware Law.  To the extent that Aventis shall be deemed to be an
           --------------
"interested stockholder" as defined in Section 203 of the Delaware General
Corporation Law (the "DGCL") solely as a result of the transactions contemplated
by this Agreement, ViroPharma has taken all action necessary to ensure that the
provisions of Section 203 of the DGCL will not be applicable to Aventis or its
Affiliates.

     4.13  Intellectual Property.  As of  August 31, 2001, the Intellectual
           ---------------------
Property that is owned by ViroPharma is owned free from any material liens or
restrictions (except as otherwise set forth in an Intellectual Property License
in respect of such Intellectual Property), and all material Intellectual
Property Licenses are in full force and effect in accordance with their terms,
and are free and clear of any material liens or restrictions, except (a) where
the failure to be free from such liens or restrictions would not have a Material
Adverse Effect, taken as a whole, or (b) as set forth in such Intellectual
Property License. As of August 31, 2001, to the Knowledge of ViroPharma, the
conduct of the business of ViroPharma, as now conducted and proposed to be
conducted under the Copromotion and Codevelopment Agreement does not infringe or
conflict with the rights of any third party in respect of any Intellectual
Property, and none of the Company Intellectual Property is being infringed by
any third party. As of August 31, 2001, there is no claim or demand of any
person or entity pertaining to, or any proceeding which is pending or, to the
Knowledge of ViroPharma, threatened, that challenges the rights of ViroPharma in
respect of any Company Intellectual Property, or that claims that any default
exists under any Intellectual Property License, except where such claim, demand
or proceeding would not materially affect the ability of ViroPharma to conduct
its business as presently conducted or proposed to be conducted under the
Copromotion and Codevelopment Agreement. For purposes of this Agreement,
"Company Intellectual Property" means the Intellectual Property that is owned by
ViroPharma and the Intellectual Property subject to an Intellectual Property
License pursuant to which its use by ViroPharma is permitted by any third party.

5.   Representations And Warranties Of Aventis.  Aventis hereby represents and
     -----------------------------------------
warrants to ViroPharma as of the date hereof and as of the Closing Date as
follows:

     5.1   Legal Power.  Aventis has the requisite corporate power to enter into
           -----------
the Transaction Documents, to carry out and perform its obligations under the
terms of the Transaction Documents.

     5.2   Due Execution.  The Transaction Documents have been duly authorized,
           -------------
executed and delivered by Aventis, and, upon due execution and delivery by
ViroPharma, each of the Transaction Documents will be a valid and binding
agreement of Aventis, except as enforceability may be limited by bankruptcy,
insolvency, reorganization, moratorium or similar laws affecting creditors'
rights generally or by equitable principles.

     5.3   Ownership.  As of the date hereof, Aventis and its Affiliates do not
           ---------
currently own greater than one percent (1%) of the outstanding Voting Stock of
ViroPharma.

________________________________________________________________________________
                                                                          Page 8
<PAGE>

     5.4   Investment Representations.  In connection with the offer, purchase
           --------------------------
and sale of the Shares, Aventis makes the following representations:

           (a)  Aventis is acquiring the Shares for its own account, not as
nominee or agent, for investment and not with a view to, or for resale in
connection with, any distribution or public offering thereof within the meaning
of the Securities Act.

           (b)  Aventis understands that:

                (i)    the Shares have not been registered under the Securities
Act by reason of a specific exemption therefrom, that such securities may be
required to be held by it indefinitely under applicable securities laws, and
that Aventis must, therefore, bear the economic risk of such investment
indefinitely, unless a subsequent disposition thereof is registered under the
Securities Act or is exempt from such registration;

                (ii)   each certificate representing such Shares will be
endorsed with the following legend:

"THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
ACT OF 1933, AS AMENDED (THE "ACT"), OR UNDER THE SECURITIES LAWS OF CERTAIN
STATES. THESE SECURITIES ARE SUBJECT TO RESTRICTIONS ON TRANSFERABILITY AND
RESALE AND MAY NOT BE TRANSFERRED OR RESOLD EXCEPT AS PERMITTED UNDER THE ACT
AND ANY APPLICABLE STATE SECURITIES LAWS, PURSUANT TO REGISTRATION OR EXEMPTION
THEREFROM OR UNLESS THE COMPANY HAS RECEIVED AN OPINION OF COUNSEL SATISFACTORY
TO THE COMPANY AND ITS COUNSEL THAT SUCH REGISTRATION IS NOT REQUIRED."; and

                (iii)  ViroPharma will instruct its transfer agent not to
register the transfer of the Shares (or any portion thereof) unless the
conditions specified in the foregoing legends are satisfied.

           (c)  Aventis has such knowledge and experience in financial or
business matters that it is capable of evaluating the merits and risks of the
investment in the Shares to be purchased hereunder.

           (d)  Aventis is an "accredited investor" as such term is defined in
Rule 501(a) of the rules and regulations promulgated under the Securities Act.

6.   Conditions To Closing.
     ---------------------

     6.1   Conditions to Obligations of Aventis at the Closing.  Aventis's
           ---------------------------------------------------
obligation to purchase the Shares at the Closing is subject to the fulfillment
to its reasonable satisfaction, on or prior to the Closing, of all of the
following conditions, any of which may be waived by Aventis:

________________________________________________________________________________
                                                                          Page 9
<PAGE>

           (a)  Representations and Warranties True.  The representations and
                -----------------------------------
warranties made by ViroPharma in Section 4 hereof shall be true and correct in
all material respects on the date of this Agreement and (except for those
representations and warranties that address matters as of a particular date
which only need be true and correct as of such date) the Closing Date with the
same force and effect as if they had been made on and as of said date, and a
certificate duly executed by an officer of ViroPharma, to the effect of the
foregoing, shall be delivered to Aventis.

           (b)  Performance of Obligations.  ViroPharma shall have performed and
                --------------------------
complied with all obligations and conditions herein required to be performed or
complied with by it on or prior to the Closing and a certificate duly executed
by an officer of ViroPharma, to the effect of the foregoing, shall be delivered
to Aventis.

           (c)  Proceedings and Documents.  All corporate and other proceedings
                -------------------------
in connection with the transactions contemplated at the Closing and all
documents and instruments incident to such transactions shall be reasonably
satisfactory in substance and form to Aventis, and Aventis shall have received
all such counterpart originals or certified or other copies of such documents as
it may reasonably request.

           (d)  Qualifications; Legal Investment.  All authorizations,
                --------------------------------
approvals, or permits, if any, of any governmental authority or regulatory body
of the United States or of any state that are required in connection with the
lawful sale and issuance of the Shares shall have been duly obtained and shall
be effective on and as of the Closing. No stop order or other order enjoining
the sale of the Shares shall have been issued and no proceedings for such
purpose shall be pending or, to the Knowledge of ViroPharma, threatened by the
SEC.

           (e)  Nasdaq Listing.  If required by Nasdaq, the Shares shall have
                --------------
been approved for listing on the Nasdaq Stock Market, subject only to official
notice of issuance. In addition, ViroPharma's Common Stock shall be listed for
trading on the Nasdaq National Market or other national securities exchange or
automated quotation system.

     6.2   Conditions to Obligations of ViroPharma at the Closing.  ViroPharma's
           ------------------------------------------------------
obligation to issue and sell the Shares at the Closing is subject to the
fulfillment to its reasonable satisfaction, on or prior to the Closing, of the
following conditions, any of which may be waived by ViroPharma:

           (a)  Representations and Warranties True.  The representations and
                -----------------------------------
warranties made by Aventis in Section 5 hereof shall be true and correct in all
material respects on the Closing Date with the same force and effect as if they
had been made on and as of said date, and a certificate duly executed by an
officer of Aventis, to the effect of the foregoing, shall be delivered to
ViroPharma.

           (b)  Performance of Obligations.  Aventis shall have performed and
                --------------------------
complied with all agreements and conditions herein required to be performed or
complied with by it on or before the Closing, and a certificate duly executed by
an officer of Aventis, to the effect of the foregoing, shall be delivered to
ViroPharma.

________________________________________________________________________________
                                                                         Page 10
<PAGE>

           (c)  Qualifications; Legal Investment.  All authorizations,
                --------------------------------
approvals, or permits, if any, of any governmental authority or regulatory body
of the United States or of any state that are required in connection with the
lawful sale and issuance of the Shares shall have been duly obtained and shall
be effective on and as of the Closing. No stop order or other order enjoining
the sale of the Shares shall have been issued and no proceedings for such
purpose shall be pending or, to the Knowledge of ViroPharma, threatened by the
SEC.

     6.3   Condition to Obligations of each Party at the Closing.  The
           -----------------------------------------------------
obligations of ViroPharma and Aventis to consummate the transactions
contemplated to occur at the Closing shall be subject to the satisfaction prior
to Closing of the following conditions, each of which may be waived by the other
party only if it is legally permitted to do so.

           (a)  HSR and Other Approvals.  Any applicable waiting period under
                -----------------------
the HSR Act relating to the transactions contemplated hereby shall have expired
or been terminated, and all other material authorizations, consents, orders or
approvals of, or regulations, declarations or filings with, or expirations of
applicable waiting periods imposed by, any Governmental Entity (including,
without limitation, any foreign antitrust filing) necessary for the consummation
of the transactions contemplated hereby, shall have been obtained or filed or
shall have occurred.

           (b)  No Litigation, Injunctions or Restraints.  No statute, rule,
                ----------------------------------------
regulation, executive order, decree, temporary restraining order, preliminary or
permanent injunction or other order enacted, entered, promulgated, enforced or
issued by any governmental entity or other legal restraint or prohibition
preventing the consummation of the transactions contemplated by this Agreement
and the Registration Rights Agreement shall be in effect.

           (c)  Copromotion and Codevelopment Agreement.  The Copromotion and
                ---------------------------------------
Codevelopment Agreement shall continue to be in full force and effect.

           (d)  Triggering Event.  The Triggering Event shall have occurred.
                -----------------

7.   Registration Rights.
     -------------------

     7.1   Piggyback Registrations. ViroPharma shall notify all Holders of
           -----------------------
Registrable Securities in writing at least thirty (30) days prior to the filing
of any Registration Statement (the "Registration Notice"), other than an
Excluded Registration Statement, under the Securities Act for purposes of a
public offering of Common Stock of ViroPharma (including, but not limited to,
Registration Statements relating to secondary offerings of Common Stock of
ViroPharma), and will afford each such Holder an opportunity to include in such
Registration Statement (other than an Excluded Registration Statement) all or
part of such Registrable Securities held by such Holder. Each Holder desiring to
include in any such Registration Statement all or any part of the Registrable
Securities held by it shall, within twenty (20) days after receiving the
Registration Notice from ViroPharma, so notify ViroPharma in writing. Such
notice shall state the intended method of disposition of the Registrable
Securities by such Holder. If a Holder does not elect to include all of its
Registrable Securities in any Registration Statement thereafter filed by
ViroPharma, such Holder shall nevertheless continue to have the right to include
any Registrable

________________________________________________________________________________
                                                                         Page 11
<PAGE>

Securities in any subsequent Registration Statement or Registration Statements
as may be filed by ViroPharma with respect to offerings of its securities (other
than an Excluded Registration Statement), all upon the terms and conditions set
forth herein.

           (a)  Underwriting.  If the Registration Statement under which
                ------------
ViroPharma gives notice under this Section 7.1 is for an underwritten offering,
ViroPharma shall so advise the Holders of Registrable Securities. In such event,
the right of any such Holder to be included in a registration pursuant to this
Section 7.1 shall be conditioned upon such Holder's participation in such
underwriting and the inclusion of such Holder's Registrable Securities in the
underwriting to the extent provided herein. All Holders proposing to distribute
their Registrable Securities through such underwriting shall enter into an
underwriting agreement in customary form, reasonably acceptable to such Holder,
with the underwriter or underwriters selected for such underwriting by
ViroPharma, including the indemnification provisions thereof. Notwithstanding
any other provision of the Agreement, if the underwriter determines in good
faith that marketing factors require a limitation of the total number of shares
to be underwritten, ViroPharma and its underwriters shall allocate the number of
Registrable Securities requested to be registered by each of the Holders as
follows: (i) first, to ViroPharma; and (ii) second, to the Holders of
Registrable Securities that have elected to participate in such offering and
such other holders of ViroPharma's capital stock who have been granted
"piggyback" registration rights prior to the date hereof and who have elected to
participate in such offering on a pro rata basis. The Holders of Registrable
Securities acknowledge that the number of securities which may be registered
pursuant to this Section 7 may be reduced to zero. ViroPharma shall have no
obligation under this Section 7 to make any offering of its securities, or to
complete an offering of its securities that it proposes to make, and shall incur
no liability to any Holder for its failure to do so.

           (b)  Right To Terminate Registration.  ViroPharma shall have the
                -------------------------------
right to terminate or withdraw any registration initiated by it under this
Section 7.1 prior to the effectiveness of such registration whether or not any
Holder has elected to include securities in such registration, provided that any
such termination or withdrawal shall not relieve ViroPharma of its obligation to
pay for the Registration Expenses incurred and shall be without prejudice to the
Holder's rights under this Section 7 to include such securities in a future
Registration Statement.

     7.2   Expenses Of Registration.  Except as specifically provided herein,
           ------------------------
all Registration Expenses incurred in connection with any registration,
qualification or compliance pursuant to Section 7.1 shall be borne by
ViroPharma, and Selling Expenses incurred in connection with any registration
hereunder shall be borne by the Holders of the securities so registered pro rata
on the basis of the number of securities so registered.

     7.3   Obligations Of ViroPharma.  The obligations of ViroPharma to effect
           -------------------------
the registration of any Registrable Securities pursuant to this Section 7 shall
at all times be subject to the restrictions set forth in Section 8.1. Whenever
required to effect such a registration, ViroPharma shall, as expeditiously as
reasonably possible:

________________________________________________________________________________
                                                                         Page 12
<PAGE>

           (a)  Prepare and file with the SEC the requisite registration
statement to effect such registration (including such audited financial
statements as may be required by the Securities Act or the rules and regulations
promulgated thereunder) and thereafter use its reasonable efforts to cause such
registration statement to become and remain effective for a period of time
sufficient to permit distribution of the Registrable Securities as provided in
such Registration Statement.

           (b)  Prepare and file with the SEC such amendments, post-effective
amendments and supplements to such Registration Statement and the prospectus
used in connection therewith as may be necessary to keep such Registration
Statement effective and to comply with the provisions of the Securities Act with
respect to the disposition of all securities covered by such Registration
Statement.

           (c)  Furnish to each Holder of Registrable Securities covered by such
Registration Statement and each underwriter, if any, of the securities being
sold by such Holder such number of conformed copies of such Registration
Statement and of each amendment and supplement thereto (in each case including
all exhibits to such Registration Statement), such number of copies of the
prospectus contained in such Registration Statement (including each preliminary
prospectus and any summary prospectus) and any prospectus filed pursuant to Rule
424 under the Securities Act and such other documents, as such Holder and
underwriter, if any, may reasonably request in order to facilitate the public
sale or other disposition of the Registrable Securities owned by such Holder (it
being understood that ViroPharma consents to the use of the prospectus and any
amendments or supplement thereto by each Holder of Registrable Securities
covered by the Registration Statement and the underwriter or underwriters, if
any, in connection with the offering and sale of Registrable Securities covered
by the prospectus or any amendment or supplement thereto).

           (d)  Use its reasonable efforts to register or qualify all
Registrable Securities under the securities laws or blue sky laws of the
jurisdictions as any Holder thereof and any underwriter of the securities being
sold by such Holder shall reasonably request, to keep such registrations or
qualifications in effect for so long as such registration statement remains in
effect, and take any other action which may be reasonably necessary or advisable
to enable such Holder and underwriter to consummate the disposition in such
jurisdictions of the securities owned by such Holder, except that ViroPharma
shall not for any such purpose be required to qualify generally to do business
as a foreign corporation or become subject to taxation in any jurisdiction
wherein it would not, but for the requirements of this subsection (d), be
obligated to be so qualified, or subject to consent to general service of
process in any such jurisdiction.

           (e)  In the event of any underwritten public offering, enter into and
perform its obligations under an underwriting agreement, in usual and customary
form, with the managing underwriter(s) of such offering. Each Holder
participating in such underwriting shall also enter into and perform its
obligations under such an agreement. In addition, ViroPharma shall, upon the
request of the managing underwriter, make available appropriate ViroPharma
management to participate in customary selling efforts or "road shows," as
appropriate.

________________________________________________________________________________
                                                                         Page 13
<PAGE>

           (f)  ViroPharma will notify each Holder of Registrable Securities
covered by such Registration Statement at any time when a prospectus relating
thereto is required to be delivered under the Securities Act, upon ViroPharma's
discovery that, or upon the happening of any event as a result of which the
prospectus included in such registration statement, as then in effect, includes
an untrue statement of a material fact or omits to state any material fact
required to be stated therein or necessary to make the statements therein not
misleading in the light of the circumstances under which they were made, and at
the request of such Holder promptly prepare and furnish to such Holder and each
underwriter, in any, a reasonable number of copies of a supplement to or an
amendment of such prospectus as may be necessary so that, as thereafter
delivered to the purchasers of such securities, such prospectus shall not
include an untrue statement of a material fact or omit to state a material fact
required to be stated therein or necessary to make the statements therein not
misleading in the light of the circumstances then existing.

           (g)  Furnish, at the request of the Holders participating in the
registration, on the date that such Registrable Securities are delivered to the
underwriters for sale: (i) an opinion, dated as of such date, of the counsel
representing ViroPharma for the purposes of such registration, in form and
substance as is customarily given to underwriters in an underwritten public
offering, addressed to the underwriters, and (ii) a letter dated as of such
date, from the independent certified public accountants of ViroPharma, in form
and substance as is customarily given by independent certified public
accountants to underwriters in an underwritten public offering, addressed to the
underwriters.

           (h)  ViroPharma will cause all Registrable Securities covered by the
Registration Statement to be listed on each securities exchange or traded or
quoted on each market on which the same class of securities issued by ViroPharma
are then listed, traded or quoted.

           (i)  ViroPharma will provide a transfer agent and a CUSIP number for
all Registrable Securities no later than the effective date of such Registration
Statement.

     7.4   Delay Of Registration; Furnishing Information.
           ---------------------------------------------

           (a)  No Holder shall have any right to obtain or seek an injunction
restraining or otherwise delaying any such registration as the result of any
controversy that might arise with respect to the interpretation or
implementation of this Section 7.

           (b)  It shall be a condition precedent to the obligations of
ViroPharma to take any action pursuant to Section 7.1 that the selling Holders
shall furnish to ViroPharma such information regarding themselves, the
Registrable Securities held by them and the intended method of disposition of
such securities as shall be legally required under the Securities Act to effect
the registration of their Registrable Securities.

________________________________________________________________________________
                                                                         Page 14
<PAGE>

     7.5  Indemnification; Contribution
          -----------------------------

          (a)  ViroPharma shall indemnify and hold harmless each Holder
(including the employees, officers and directors of Aventis) from and against
any and all losses, claims, damages, liabilities and expenses (including
reasonable costs of investigation) arising out of or based upon any untrue, or
allegedly untrue, statement of a material fact contained in any Registration
Statement, prospectus or preliminary prospectus or notification or offering
circular (as amended or supplemented if ViroPharma shall have furnished any
amendments or supplements thereto) or arising out of or based upon any omission
or alleged omission to state therein a material fact required to be stated
therein or necessary to make the statements therein not misleading, except
insofar as the same are caused by or contained in any information concerning
such Holder furnished in writing to ViroPharma by such Holder expressly for use
in such Registration Statement.

          (b)  Each Holder shall indemnify and hold harmless ViroPharma, any
underwriter retained by ViroPharma and their respective directors, officers,
employees and each Person who controls ViroPharma or such underwriter (within
the meaning of the Securities Act and the Exchange Act) from and against any and
all losses, claims, damages, liabilities and expenses (including reasonable
costs of investigation) arising out of or based upon any untrue, or allegedly
untrue, statement of a material fact contained in any Registration Statement,
prospectus or preliminary prospectus or notification or offering circular (as
amended or supplemented if ViroPharma shall have furnished any amendments or
supplements thereto) or arising out of or based upon any omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make the statements therein not misleading, if such statement or
omission was made in reliance upon and in conformity with any information
concerning such Holder furnished in writing to ViroPharma by such Holder
specifically for use in the preparation of such Registration Statement or
prospectus; provided, however, that the total amount to be indemnified by such
            --------  -------
Holder pursuant to this Section 7.5(b) shall be limited to the net proceeds
received by the Holders in the offering to which the Registration Statement or
prospectus relates.

          (c)  Each Person entitled to indemnification hereunder (the
"Indemnified Party") agrees to give prompt written notice to the indemnifying
party (the "Indemnifying Party") after the receipt by the Indemnified Party of
any written notice of the commencement of any action, suit, proceeding or
investigation or threat thereof made in writing for which the Indemnified Party
intends to claim indemnification or contribution pursuant to this Agreement;
provided, however, that the failure to so notify the Indemnifying Party shall
--------  -------
not relieve the Indemnifying Party of any liability that it may have to the
Indemnified Party hereunder unless, and only to the extent that, such failure
results in the Indemnifying Party's forfeiture of substantive rights or
defenses. If notice of commencement of any such action is given to the
Indemnifying Party as above provided, the Indemnifying Party shall be entitled
to participate in and, to the extent it may wish, jointly with any other
Indemnifying Party similarly notified, to assume the defense of such action at
its own expense, with counsel chosen by it and reasonably satisfactory to such
Indemnified Party. The Indemnified Party shall have the right to employ separate
counsel in any such action and participate in the defense thereof, but the fees
and expenses of such counsel (other than reasonable costs of investigation)
shall be paid by the Indemnified Party unless (i) the Indemnifying Party agrees
to pay the same, (ii) the Indemnifying

________________________________________________________________________________
                                                                         Page 15
<PAGE>

Party fails to assume the defense of such action with counsel reasonably
satisfactory to the Indemnified Party in its reasonable judgment or (iii) the
named parties to any such action (including any impleaded parties) have been
advised by such counsel that either (x) representation of such Indemnified Party
and the Indemnifying Party by the same counsel would be inappropriate under
applicable standards of professional conduct or (y) there may be one or more
legal defenses available to it which are different from or additional to those
available to the Indemnifying Party. In either of such cases, the Indemnifying
Party shall not have the right to assume the defense of such action on behalf of
such Indemnified Party. No Indemnifying Party shall be liable for any settlement
entered into without its written consent (other than in the case where the
Indemnifying Party is unconditionally released from liability and its rights are
not adversely effected), which consent shall not be unreasonably withheld.

          (d)  If the indemnification provided for in this Section 7.5 from the
Indemnifying Party pursuant to applicable law is unavailable to an Indemnified
Party hereunder in respect of any losses, claims, damages, liabilities or
expenses referred to therein, then the Indemnifying Party, in lieu of
indemnifying such Indemnified Party, shall contribute to the amount paid or
payable by such Indemnified Party as a result of such losses, claims, damages,
liabilities or expenses in such proportion as is appropriate to reflect the
relative fault of the Indemnifying Party and Indemnified Party in connection
with the actions which resulted in such losses, claims, damages, liabilities or
expenses, as well as any other relevant equitable considerations. The relative
faults of such Indemnifying Party and Indemnified Party shall be determined by
reference to, among other things, whether any action in question, including any
untrue or alleged untrue statement of a material fact or omission or alleged
omission to state a material fact, has been made by, or relates to information
supplied by, such Indemnifying Party or Indemnified Party, and the parties'
relative intent, knowledge, access to information and opportunity to correct or
prevent such action. The amount paid or payable by a party as a result of the
losses, claims, damages, liabilities and expenses referred to above shall be
deemed to include, subject to the limitations set forth in Sections 7.5(a), (b)
and (c), any legal or other fees, charges or expenses reasonably incurred by
such party in connection with any investigation or proceeding. The parties
hereto agree that it would not be just and equitable if contribution pursuant to
this Section 7.5(d) were determined by pro rata allocation or by any other
method of allocation which does not take account of the equitable considerations
referred to in the immediately preceding paragraph. No Person guilty of
fraudulent misrepresentation (within the meaning of Section 11(f) of the
Securities Act) shall be entitled to contribution from any Person.

     7.6  Assignment Of Registration Rights.  The rights to cause ViroPharma to
          ---------------------------------
register Registrable Securities pursuant to this Section 7 may only be assigned
by Aventis to a transferee or assignee of Registrable Securities that is an
Affiliate or a successor (by operation of law or otherwise) to substantially all
the business or assets of Aventis; provided, however (i) Aventis shall, within
ten (10) days after such transfer, furnish to ViroPharma written notice of the
name and address of such transferee or assignee and the securities with respect
to which such registration rights are being assigned, and (ii) such transferee
shall agree to be subject to all restrictions with respect to the Shares set
forth in this Agreement.

     7.7  "Market Stand-Off" Agreement.  If requested by ViroPharma or the
          ----------------------------
representative of the underwriters of Common Stock (or other securities) of
ViroPharma, each

________________________________________________________________________________
                                                                         Page 16
<PAGE>

Holder shall agree not to sell or otherwise transfer or dispose of any Common
Stock (or other securities) of ViroPharma held by such Holder (other than those
included in the registration, if any) for a period commencing on the date that
such Holder receives the Registration Notice (but in no case earlier than thirty
(30) days prior to the date of the filing of the applicable Registration
Statement) and continuing for the period specified by the [Brepresentative of
the underwriters not to exceed ninety (90) days following the effective date of
a Registration Statement of ViroPharma filed under the Securities Act, provided
that all executive officers and directors of ViroPharma enter into similar
agreements. Notwithstanding the foregoing, Aventis shall have no obligations
under this Section 7.7: (a) in respect of a private placement by Aventis of any
Common Stock (or other securities) of ViroPharma to the extent that such private
placement occurs prior to the filing of the applicable Registration Statement,
(b) from and after the date that Aventis's registration rights granted hereunder
have terminated in their entirety, or (c) if fifty percent (50%) or more of
Common Stock requested by such Holder to be included in such registration is
excluded under Section 7.1(a).

     7.8  Termination Of Registration Rights.  This Section 7 and the
          ----------------------------------
registration rights granted hereunder in respect of the Shares shall terminate
in their entirety on the later of (i) five (5) years from the Closing Date, or
(ii) three (3) months after the Holder ceases to be an "affiliate" (within the
meaning of the Exchange Act or Securities Act) of ViroPharma.

8.   Covenants
     ---------

     8.1  Covenant Of Aventis.  Aventis hereby covenants and agrees that it
          -------------------
shall not exercise the registration rights described in Section 7 during the one
(1) year period following the Closing Date.

     8.2  Covenant Of ViroPharma.
          ----------------------

          (a)  ViroPharma hereby covenants and agrees that it shall take all
necessary and appropriate actions to ensure that it shall have available under
its Restated Certificate of Incorporation as in effect on the Closing Date
sufficient authorized but unissued shares of its Common Stock to issue and sell
to Aventis all of the Shares.

          (b)  ViroPharma will file with Nasdaq all documentation required by
Nasdaq, if any, in connection with the issuance of the Shares.

     8.3  Rights Agreement.  In the event that the purchase of the Shares
          ----------------
hereunder by Aventis at any Closing would cause Aventis to become an "Acquiring
Person," as such term is defined in the Rights Agreement, because either (a) the
Shares, by themselves, constitute in excess of twenty percent (20%) of then-
outstanding Common Stock of ViroPharma (the "Threshold"), or (b) after the date
hereof but prior to the Closing Date Aventis acquires a third party that owns
capital stock of ViroPharma and whose ownership of capital stock of ViroPharma
is not the primary business purpose of such third party (the "Third Party
ViroPharma Stock"), and when the Shares are added together with Third Party
ViroPharma Stock, Aventis's aggregate beneficial ownership exceeds the
Threshold, then prior to the

________________________________________________________________________________
                                                                         Page 17
<PAGE>

consummation of the Closing, ViroPharma shall cause the Rights Agreement to be
amended to ensure that the acquisition of the Shares at such Closing does not
cause Aventis to become an Acquiring Person. Notwithstanding the foregoing,
nothing in this Section 8.3 shall require ViroPharma to amend the Rights
Agreement if Aventis's purchase of the Shares would result in Aventis becoming
an Acquiring Person because such Shares, when added to any shares of the capital
stock of ViroPharma acquired by Aventis other than under this Agreement or as
specifically described in clause (b) of this Section 8.3, causes Aventis's
ownership to exceed the Threshold.

     8.4  Notice of Market Sale.  Aventis shall provide ViroPharma with a notice
          ---------------------
of its intent to sell the Shares pursuant to Rule 144 prior to completing such a
sale in order to provide ViroPharma an opportunity to arrange an orderly
disposition of the Shares. At any point during such thirty (30) day period,
ViroPharma may terminate the remainder of such period and notify Aventis that
Aventis may sell the Shares pursuant to Rule 144. Notwithstanding the foregoing,
Aventis shall have no obligations under this Section 8.4 in respect of a private
placement by Aventis of the Shares.

9    Termination.
     -----------

     9.1  Termination.  This Agreement may be terminated at any time prior to
          -----------
the Closing:

          (a)  by mutual written consent of Aventis and ViroPharma;

          (b)  by Aventis or ViroPharma:

               (i)     if the Closing shall not have occurred prior to the
expiration of the one hundred fifteen (115) day period following the date of the
Triggering Event; provided that the right to terminate this Agreement pursuant
to this clause shall not be available to a party whose failure to fulfill an
obligation under this Agreement results in the failure of the Closing to occur;

               (ii)    if there shall be any statute, law, regulation or rule
that makes consummating the transactions contemplated hereby illegal or if any
court or other Governmental Entity of competent jurisdiction shall have issued
judgment, order, decree or ruling, or shall have taken such other action
restraining, enjoining or otherwise prohibiting the consummation of the
transactions contemplated hereby and such judgment, order, decree or ruling
shall have become final and non-appealable;

               (iii)   if the Copromotion and Codevelopment Agreement shall have
terminated; or

               (iv)    the United States Federal Trade Commission ("FTC") and/or
the United States Department of Justice shall seek a preliminary injunction
under the HSR Act against ViroPharma and Aventis to enjoin the transactions
contemplated by this Agreement or the Copromotion and Codevelopment Agreement;
or

________________________________________________________________________________
                                                                         Page 18
<PAGE>

           (c)  by Aventis:

                (i)     if ViroPharma shall have (A) failed to perform any of
its material obligations contained herein, or (B) breached any of its material
representations or warranties contained herein, provided that Aventis gives
ViroPharma written notice of such failure to perform or breach and ViroPharma
does not cure such failure to perform or breach within thirty (30) days after
its receipt of such written notice;

                (ii)    if any of the conditions set forth in Section 6.1 or 6.3
(other than 6.3(a)) shall become impossible to fulfill (other than as a result
of any breach by Aventis of the terms of this Agreement) and shall not have been
waived in accordance with the terms of this Agreement; or

                (iii)   if the Common Stock shall no longer be listed for
trading on the Nasdaq National Market or other national securities exchange or
automated quotation system; provided however, that Aventis may not terminate
this Agreement pursuant to this Section 8.1(c)(iii): (A) prior to the date of
the Triggering Event; and (B) on or after the date of the Triggering Event, if
ViroPharma shall become listed for trading on the Nasdaq National Market or
other national securities exchange or automated quotation system at any time
during the ninety (90) day period after the date of the Triggering Event.

           (d)  by ViroPharma:

                (i)     if Aventis shall have (A) failed to perform any of its
material obligations contained herein, or (B) breached any of its material
representations or warranties contained herein, provided that ViroPharma gives
Aventis written notice of such failure to perform or breach and Aventis does not
cure such failure to perform or breach within thirty (30) days after its receipt
of such written notice; or

                (ii)    if any of the conditions set forth in Section 6.2 or 6.3
shall become impossible to fulfill (other than as a result of any breach by
ViroPharma of the terms of this Agreement) and shall not have been waived in
accordance with the terms of this Agreement.

     9.2   Effect of Termination.  In the event of termination of this Agreement
           ---------------------
by either Aventis or ViroPharma as provided in Section 9.1, this Agreement shall
forthwith become void and have no effect, without any liability or obligation on
the part of Aventis or ViroPharma, other than the provisions of this Section
9.2, and except to the extent that such termination results from a material
breach by a party of its representations, warranties, covenants or agreements
set forth in this Agreement.

10.  Miscellaneous.
     -------------

     10.1  Governing Law.  This Agreement shall be governed by and construed in
           -------------
accordance with the laws of the Commonwealth of Pennsylvania, without regard to
the choice of law provisions thereof, and the federal laws of the United States.

________________________________________________________________________________
                                                                         Page 19
<PAGE>

     10.2  Public Statements.  Any statement to the public regarding this
           -----------------
Agreement shall be approved in advance by ViroPharma and Aventis, except as
otherwise required by law. Notwithstanding the foregoing, Aventis acknowledges
that ViroPharma shall file this Agreement with the SEC.

     10.3  Successors And Assigns.  Except as otherwise expressly provided
           ----------------------
herein, the respective rights and obligations of either Party under this
Agreement shall not be assignable in whole or in part by a Party without the
prior written consent of the other Party, which consent shall not be
unreasonably withheld or delayed. Notwithstanding the preceding sentence, in
connection with the merger, acquisition, transfer of all or substantially all of
a Party's assets or other change in control of either Party, such Party may
assign its rights and obligations under this Agreement in whole or in part to
such Party's transferee or successor in interest without the prior written
consent of the other Party. This Agreement shall bind and inure to the benefit
of Parties and their permitted successors and assigns.

     10.4  Entire Agreement.  This Agreement, the Copromotion and Codevelopment
           ----------------
Agreement and the exhibits thereto, that certain Mutual Non-Disclosure Agreement
dated as of March 1, 2001 between the ViroPharma and Aventis and that certain
Letter Agreement dated April 17, 2001 between ViroPharma and Aventis and the
other documents delivered pursuant hereto, constitute the full and entire
understanding and agreement among the Parties with regard to the subjects hereof
and no Party shall be liable or bound to any other Party in any manner by any
representations, warranties, covenants, or agreements except as specifically set
forth herein or therein. Nothing in this Agreement, express or implied, is
intended to confer upon any Party, other than the parties hereto and their
respective successors and assigns, any rights, remedies, obligations, or
liabilities under or by reason of this Agreement, except as expressly provided
herein.

     10.5  Separability.  In the event any provision of this Agreement shall be
           ------------
invalid, illegal, or unenforceable, it shall to the extent practicable, be
modified so as to make it valid, legal and enforceable and to retain as nearly
as practicable the intent of the Parties, and the validity, legality, and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.

     10.6  Amendment And Waiver.  Except as otherwise provided herein, any term
           --------------------
of this Agreement may be amended and the observance of any term of this
Agreement may be waived (either generally or in a particular instance, either
retroactively or prospectively, and either for a specified period of time or
indefinitely), with the written consent of ViroPharma and Aventis. Any amendment
or waiver effected in accordance with this Section shall be binding upon any
holder of any securities purchased under this Agreement (including securities
into which such securities have been converted), each future holder of all such
securities, and ViroPharma.

     10.7  Notices. All notices, requests, or other communications given
           -------
hereunder shall be in writing and shall be deemed to have been duly given if (a)
delivered by hand; (b) mailed by registered or certified mail; (c) sent by air
courier; or (d) sent by cable, telex or facsimile, followed within twenty-four
(24) hours by notification pursuant to (a), (b) or (c) above, in each

________________________________________________________________________________
                                                                         Page 20
<PAGE>

case to the address set forth below or to such other address as a Party may
specify for itself by written notice given as aforesaid.

     If to Aventis:           Pharma Inc.
                              2150 Saint Elzear Blvd. West
                              Laval, Quebec, Canada
                              H7L 4A8
                              FAX: 514-956-4192
               Attention:     Vice-President, Finance
                              and Information Solutions

    with a copy to:           Aventis Pharma Inc.
                              2150 Saint Elzear Blvd. West
                              Laval, Quebec, Canada
                              H7L 4A8
                              FAX: 514-956-6171
                              Attention:    General Counsel

            and to:           Aventis Pharmaceuticals Inc.
                              Route 202-206
                              P.O. Box 6800
                              Bridgewater, NJ 08807, U.S.A.
                              Facsimile: 1-908-231-4480
                              Attention:    Vice President, Legal Department

  If to ViroPharma:           ViroPharma Incorporated
                              405 Eagleview Boulevard
                              Exton, PA 19341
                              FAX: 610-458-7380
                              Attention:    Chief Financial Officer

    with a copy to:           ViroPharma Incorporated
                              405 Eagleview Boulevard
                              Exton, PA 19341
                              FAX: 610-458-7380
                              Attention:    General Counsel

     10.8  Fees And Expenses.  ViroPharma and Aventis shall each bear their own
           -----------------
expenses and legal fees incurred on their behalf with respect to this Agreement
and the transactions contemplated hereby.

     10.9  Titles And Subtitles.  The titles of the Sections and subsections of
           --------------------
this Agreement are for convenience of reference only and are not to be
considered in construing this Agreement.

________________________________________________________________________________
                                                                         Page 21
<PAGE>

     10.10  Counterparts.  This Agreement may be executed in any number of
            ------------
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one instrument.

IN WITNESS WHEREOF, this Stock Purchase Agreement is hereby executed as of the
date first above written.

                              VIROPHARMA INCORPORATED

                              By:    Exhibit Only - Not For Signature
                                   ----------------------------------
                                   Michel de Rosen
                                   President and CEO

                              AVENTIS PHARMA INC.

                              By:    Exhibit Only - Not For Signature
                                   ----------------------------------
                                   Jean-Francois Leprince
                                   President

________________________________________________________________________________
                                                                         Page 22
<PAGE>

                 Exhibit 4.1 (To the Stock Purchase Agreement)

           Exceptions to Capitalization Representation and Warranty
           --------------------------------------------------------

Certain preemptive rights were granted pursuant to that certain Investment
Agreement dated May 5, 1999 between ViroPharma Incorporates and PSV, LP (f/k/a
Perseus-Soros BioPharmaceutical Fund, LP).

Common Stock subject to sale pursuant to that certain Stock Purchase Agreement
dated as of December 9, 1999 between ViroPharma Incorporated and American Home
Products Corporation.

________________________________________________________________________________
                                                                         Page 23<PAGE>

                                                                   Exhibit 10.36

                           STOCK PURCHASE AGREEMENT

     THIS STOCK PURCHASE AGREEMENT (this "Agreement") is made as of September 9,
2001, by and between ViroPharma Incorporated ("ViroPharma"), a Delaware
corporation with its principal place of business at 405 Eagleview Boulevard,
Exton, PA 19341, and Aventis Pharma Inc., a Canadian corporation with its
principal place of business at 2150 Saint Elzear Boulevard West, Laval, Quebec,
Canada, H7L 4A8 ("Aventis").

                                   RECITALS
                                   --------

     WHEREAS, ViroPharma and an Affiliate of Aventis have entered into that
certain Copromotion and Codevelopment Agreement dated September 9, 2001 (the
"Copromotion and Codevelopment Agreement"); and

     WHEREAS, in connection with the execution of the Copromotion and
Codevelopment Agreement, ViroPharma desires to sell to Aventis and Aventis
desires to purchase from ViroPharma shares of common stock of ViroPharma on the
terms and subject to the conditions set forth in this Agreement.

     NOW, THEREFORE, in consideration of the foregoing recitals and the mutual
covenants and agreements contained herein, the Parties hereto, intending to be
legally bound, do hereby agree as follows:

1.   Definitions.  The capitalized terms used herein shall have the meanings
     -----------
ascribed to them below, provided that capitalized terms used herein that are not
defined herein shall have the meanings ascribed to them in the Copromotion and
Codevelopment Agreement:

     1.1  "Affiliate" means any person or entity that directly or indirectly
           ---------
controls or is controlled by or is under common control with ViroPharma or
Aventis, as the case may be, but only for so long as said control shall
continue. As used herein the term "control" means the direct or indirect
ownership of over fifty percent (50%) of the outstanding voting securities of an
entity, or the right to receive over fifty percent (50%) of the profits or
earnings of an entity (or, in either case, such lesser percentage which is the
maximum allowed to be owned by a foreign corporation in a particular
jurisdiction). Such other relationship as in fact gives such individual or
entity the power or ability to control the management, business and affairs of
an entity shall also be deemed to constitute control.

     1.2  "Closing" has the meaning ascribed to it in Section 3.1 hereof.
           -------

     1.3  "Closing Date" means the day on which the transaction that is the
           ------------
subject of such Closing is consummated.

     1.4  "Common Stock" means the common stock of ViroPharma, par value $0.002
           ------------
per share.
<PAGE>

     1.5  "Deemed Market Price" has the meaning ascribed to it in Section 2
           -------------------
hereof.

     1.6  "Exchange Act" means the Securities Exchange Act of 1934, as amended,
           ------------
together with the rules and regulations promulgated thereunder.

     1.7  "Excluded Registration Statements" means (a) Registration Statements
           --------------------------------
on Form S-8 (or any successor or similar form) relating to employee benefit
plans, (b) Registration Statements on Form S-4 (or any successor or similar
form) relating to corporate reorganizations or other transactions under Rule 145
of the Securities Act, or (c) Registration Statements covering shares of
ViroPharma's capital stock issued pursuant to that certain Investment Agreement
(the "Perseus Shares") dated May 5, 1999 between ViroPharma and PSV, LP
(previously known as Perseus-Soros BioPharmaceutical Fund, LP) (the "Perseus
Agreement"), and any Common Stock issued upon conversion of the Perseus Shares
or upon exercise of warrants issued pursuant to the Perseus Agreement.

     1.8  "GAAP" means generally accepted accounting principles in the United
           ----
States.

     1.9  "Holder" means each person owning of record Registrable Securities
           ------
that have not been sold to the public.

     1.10  "Intellectual Property" means trademarks, trade names, trade dress,
            ---------------------
service marks, copyrights, and similar rights (including registrations and
applications to register or renew the registration of any of the foregoing),
patents and patent applications, trade secrets, and any other similar
intellectual property rights.

     1.11  "Intellectual Property License" means any license, permit,
            -----------------------------
authorization, approval, contract or consent granted, issued by or with any
Person relating to the use of Intellectual Property.

     1.12  "Knowledge" means the knowledge of such party, assuming that such
            ---------
party engaged in reasonable inquiry or investigation with respect to the
relative subject matter.

     1.13  "Material Adverse Effect" on or with respect to an entity (or group
            -----------------------
of entities taken as a whole) means any state of facts, event, change or effect
that has had, or that might be reasonably expected to have, a material adverse
effect on the business, properties, results of operations or financial condition
of such entity (or of such group of entities taken as a whole).

     1.14  "Nasdaq" means the Nasdaq Stock Market, Inc.
            ------

     1.15  "Party" means a party to this Agreement.
            -----

     1.16  "Purchase Price" has the meaning ascribed to it in Section 2.1.
            --------------

     1.17  "Person" means any individual, firm, corporation, partnership,
            ------
limited liability company, trust, incorporated or unincorporated association,
joint venture, joint stock company,

                                       2
<PAGE>

government (or an agency or political subdivision thereof) or other entity of
any kind, and shall include any successor (by merger or otherwise) of such
entity.

     1.18  "Register," "Registered," and "Registration" refer to a registration
            --------    ----------        ------------
effected by preparing and filing a Registration Statement in compliance with the
Securities Act, and the declaration or ordering of effectiveness of such
Registration Statement or document by the SEC.

     1.19  "Registrable Securities" means (a) the Shares; and (b) any shares of
            ----------------------
Common Stock of ViroPharma or other securities issued as (or issuable upon the
conversion or exercise of any warrant, right or other security which is issued
as) a dividend or other distribution with respect to, or in exchange for or in
replacement of, the Shares by way of stock dividend, stock split or in
connection with a combination of shares, recapitalization or other
reorganization or otherwise. Notwithstanding the foregoing, as to any particular
Shares or other securities described above, once issued they shall cease to be
Registrable Securities when (x) a registration statement with respect to the
sale of such securities shall have become effective under the Securities Act and
such securities shall have been disposed of in accordance with such registration
statement, (y) they shall have been distributed pursuant to Rule 144 (or any
successor provision) under the Securities Act, or (z) they shall have been
otherwise transferred in a private transaction in which the rights under this
Section 7 hereof have not been assigned.

     1.20 "Registration Expenses" means all expenses incurred by ViroPharma in
           ---------------------
complying with Section 7.1 hereof, including, without limitation, registration
and filing fees, printing and reproduction expenses, fees and disbursement of
counsel for ViroPharma, blue sky fees and expenses, messenger and delivery
expenses, the expenses of any special audits or "comfort letters" incident to or
required by any such registration and any fees and disbursements of underwriters
customarily paid by issuers or seller of securities, but excluding Selling
Expenses.

     1.21 "Registration Statement" means a Registration Statement filed pursuant
           ----------------------
to the Securities Act.

     1.22  "Rights Agreement" means that certain Rights Agreement dated
            ----------------
September 10, 1998 between ViroPharma and StockTrans, Inc.

     1.23  "SEC Documents" means ViroPharma's Form S-3 filed with the SEC on
            -------------
July 3, 2001, its Annual Report on Form 10-K for the year ended December 31,
2000, its Quarterly Reports on Form 10-Q for the quarters ended June 30, 2001
and March 31, 2001, and its Proxy Statement for its Annual Meeting of
Stockholders held on June 11, 2001, each as filed with the SEC, but shall not
include any portion of any document which is not deemed to be filed under
applicable SEC rules and regulations.

     1.24  "SEC" means the U.S. Securities and Exchange Commission.
            ---

     1.25  "Securities Act" means the Securities Act of 1933, as amended,
            --------------
together with the rules and regulations promulgated thereunder.

                                       3
<PAGE>

     1.26  "Selling Expenses" shall mean all underwriting discounts and selling
            ----------------
commissions applicable to the sale, and all fees and expenses of counsel
exclusively for Aventis, if any.

     1.27  "Shares" means the shares of Common Stock to be acquired by Aventis
            ------
hereunder.

     1.28  "Transaction Documents" means this Agreement, the Copromotion and
            ---------------------
Codevelopment Agreement, and any other agreement or instrument executed by
ViroPharma in connection with the foregoing.

     1.29  "Triggering Event" means Regulatory Approval of an NDA in the United
            ----------------
States for a VP Product for the First Indication.

     1.30  "Voting Stock" means securities of any class or series of a
            ------------
corporation or association the holders of which are ordinarily, in the absence
of contingencies, entitled to vote generally in matters put before the
shareholders or members of such corporation or association, or securities
convertible or exchangeable into or exercisable for any such securities.

2.   Purchase and Sale.
     -----------------

     2.1  Subject to Section 2.2 below, at the Closing, ViroPharma will sell to
Aventis and Aventis will purchase from ViroPharma, for the aggregate
consideration of $20,000,000, as may be adjusted in Section 2.2 below (the
"Purchase Price"), a number of shares of Common Stock equal to the quotient of
$20,000,000 divided by the Deemed Market Price. For the purposes of this Section
2, the "Deemed Market Price" shall be equal to the average of the closing sales
prices of ViroPharma's Common Stock, as reported by Nasdaq, for those days on
which ViroPharma's Common Stock was traded during the twenty (20) trading days
ending on the trading day immediately preceding the date of the Triggering
Event; provided, however, that if ViroPharma takes the steps contemplated under
Section 9.1(c)(iii), then the Deemed Market Price shall be equal to the average
of the closing sales prices of ViroPharma's Common Stock as reported by Nasdaq
for those days on which ViroPharma's Common Stock was traded during the twenty
(20) trading days immediately following the date that ViroPharma again becomes
listed for trading as contemplated by Section 9.1(c)(iii).

     2.2  (a)  Notwithstanding the foregoing, the number of shares purchasable
hereunder shall not be in excess of nineteen and nine tenths percent (19.9%) of
the number of shares of Common Stock issued and outstanding on the date hereof,
which number shall be subject to appropriate and equitable adjustment for any
stock split, stock dividend or reclassification of the Common Stock or similar
event (the "Maximum Number of Shares"). Only shares of Common Stock acquired
pursuant to this Agreement will be included in determining whether the
limitation contained herein would be exceeded for purposes of this Section.

          (b)  In the event the number of shares to be acquired pursuant to
Section 2.1 would exceed the Maximum Number of Shares, then notwithstanding
anything to the contrary in

                                       4
<PAGE>

Section 2.1, at the Closing ViroPharma will sell to Aventis and Aventis will
purchase from ViroPharma the Maximum Number of Shares for an aggregate
consideration equal to the product of the Maximum Number of Shares times the
Deemed Market Price.

3.   Closing.
     -------

     3.1  Closing. The completion of the sale and purchase of the Shares (the
          -------
"Closing") shall be held within five (5) business days after the satisfaction of
the closing conditions set forth in Article 6, or on such other date as the
parties shall mutually agree.

     3.2  Delivery.  At the Closing, subject to the terms and conditions hereof,
          --------
Aventis shall deliver to ViroPharma the Purchase Price by wire transfer to an
account designated in writing by ViroPharma no less than two (2) business days
prior to the Closing, and ViroPharma will deliver to Aventis a stock
certificate, in the name of Aventis, representing the Shares purchased at the
Closing, dated as of the Closing Date, against payment of such Purchase Price.

     3.3  Location.  The Closing shall occur at the offices ViroPharma, unless
          --------
otherwise agreed to by the Parties.

4.   Representations and Warranties of ViroPharma. ViroPharma hereby represents
     --------------------------------------------
and warrants to Aventis as of the date hereof and as of the Closing Date (except
as set forth below), as follows:

     4.1  Capitalization.    As of August 31, 2001, the authorized capital stock
          ---------------
of ViroPharma consisted of (a) 100,000,000 shares of Common Stock, of which (i)
18,699,695 shares were issued and outstanding, (ii) up to 690,000 shares have
been reserved for issuance upon exercise of outstanding common stock warrants,
(iii) 3,750,000 shares have been reserved for issuance under ViroPharma's Stock
Option and Restricted Share Plan, (iv) 300,000 shares have been reserved for
issuance under ViroPharma's Employee Stock Purchase Plan, and (v) 1,649,107
shares have been reserved for issuance upon exercise of outstanding six percent
(6%) convertible subordinated notes; and (b) 5,000,000 shares of preferred
stock, none of which is outstanding and 200,000 shares of which have been
designated the Series A Junior Participating Preferred Shares, par vale $.01 per
share, and have been reserved for issuance pursuant to the Rights Agreement. All
issued and outstanding shares of ViroPharma's capital stock have been duly
authorized and validly issued, and are fully paid and nonassessable. As of
August 31, 2001, except as referred to in Exhibit 4.1 attached hereto, there are
no preemptive or similar rights on the part of any holder of any class or
securities of ViroPharma. As of August 31, 2001, except as set forth in the SEC
Documents, as set forth on Exhibit 4.1 attached hereto or as described or
referred to above, there are no securities convertible into or exchangeable for,
or options, warrants, calls subscriptions, rights, contracts or understandings
of any kind to which ViroPharma is a party or by which it is bound obligating
ViroPharma to issue, deliver or sell, or cause to be issued, delivered or sold
additional shares of its capital stock. As of August 31, 2001, except for the
repurchase of shares owned by employees upon termination of employment, there
are no outstanding agreement of ViroPharma to repurchase, redeem or otherwise
acquire any shares of its capital stock. As of August 31, 2001, ViroPharma does
not have any subsidiaries or any equity interest with a value of $250,000 or
more in any corporation or entity.

                                       5
<PAGE>

     4.2  Litigation.  There is no action, suit, proceeding nor, to its
          ----------
Knowledge, any investigation, pending or currently threatened against ViroPharma
that questions the validity of this Agreement or the issuance of the Common
Stock contemplated hereby, nor to its Knowledge, is there any basis therefor. As
of August 31, 2001, there is no other action, suit, or proceeding pending or, to
the Knowledge of ViroPharma, currently threatened against ViroPharma that might,
individually or in the aggregate, result in Material Adverse Effect. As of
August 31, 2001, ViroPharma is not subject to any consents, orders, decrees or
judgments of any governmental entity that, individually or in the aggregate, may
have a Material Adverse Effect.

     4.3  Organization and Good Standing. ViroPharma is a corporation duly
          ------------------------------
organized, validly existing and in good standing under the laws of the State of
Delaware and has all requisite corporate power and authority to carry on its
business as now conducted. ViroPharma is duly qualified and is in good standing
as a foreign corporation in each jurisdiction in which the properties owned,
leased or operated, or the business conducted, by it requires such qualification
except where the failure to be so qualified or in good standing, individually or
in the aggregate, would not have a Material Adverse Effect.

     4.4  Authorization.  All corporate action on the part of ViroPharma, its
          -------------
officers, directors and stockholders necessary for the authorization, execution
and delivery of the Transaction Documents have been taken. ViroPharma has the
requisite corporate power to enter into the Transaction Documents and to carry
out and perform its obligations thereunder. The Transaction Documents have been
duly authorized, executed and delivered by ViroPharma and, upon due execution
and delivery by Aventis, each Transaction Document will be a valid and binding
agreement of ViroPharma, except as enforceability may be limited by bankruptcy,
insolvency, reorganization, moratorium or similar laws affecting creditors'
rights generally or by equitable principles.

     4.5  No Conflict With Other Instruments.  The execution, delivery and
          ----------------------------------
performance of the Transaction Documents will not result in any violation of, be
in conflict with, cause any acceleration or any increased payments under, or
constitute a default under, with or without the passage of time or the giving of
notice: (a) any provision of ViroPharma's Amended and Restated Certificate of
Incorporation or Bylaws as in effect on the date hereof or at the Closing; (b)
any provision of any judgment, decree or order to which ViroPharma is a party or
by which it is bound, or (c) any note, mortgage, material contract or agreement,
or any license, waiver, exemption, order or permit.

     4.6  Disclosure Documents.
          --------------------

          (a)  ViroPharma's SEC Documents: (i) complied in all material respects
with the applicable requirements of the Securities Act or Exchange Act, as
applicable, as such requirements were in effect on the date that such SEC
Document was filed with the SEC, and (ii) when filed with the SEC, did not
contain any untrue statement of material fact or omit to state any material fact
required to be stated therein or necessary in order to make the statements
therein, in light of the circumstances under which they were made, not
misleading.

                                       6
<PAGE>

           (b)  The audited financial statements of ViroPharma included in
ViroPharma's SEC Documents comply in all material respects with the published
rules and regulations of the SEC with respect thereto, and such audited
financial statements (i) were prepared from the books and records of ViroPharma,
(ii) were prepared in accordance with GAAP applied on a consistent basis (except
as may be indicated therein or in the notes or schedules thereto) and (iii)
present fairly the financial position of ViroPharma as of the dates thereof and
the results of operations and cash flows for the periods then ended. The
unaudited financial statements included in the SEC Documents comply in all
material respects with the published rules and regulations of the SEC with
respect thereto, and such unaudited financial statements (i) were prepared from
the books and records of ViroPharma, (ii) were prepared in accordance with GAAP,
except as otherwise permitted under the Exchange Act and the rules and
regulations thereunder, on a consistent basis (except as may be indicated
therein or in the notes or schedules thereto) and (iii) present fairly the
financial position of ViroPharma as of the dates thereof and the results of
operations and cash flows (or changes in financial condition) for the periods
then ended, subject to normal year-end adjustments and any other adjustments
described therein or in the notes or schedules thereto

     4.7   Absence of Certain Events and Changes.  During the period commencing
           -------------------------------------
on December 31, 2000 and continuing through August 31, 2001, ViroPharma has
conducted its business in the ordinary course consistent with past practice and
there has not been any event, change or development which, individually or in
the aggregate, would have a Material Adverse Effect, taken as a whole.

     4.8   Compliance with Applicable Law.  As of August 31, 2001, ViroPharma is
           ------------------------------
in compliance in all material respects with all material statutes, laws,
regulations, rules, judgments, orders and decrees of all governmental entities
applicable to it that relate to its business, and ViroPharma has not received
any notice alleging noncompliance except, with reference to all the foregoing,
where the failure to be in compliance would not, individually or in the
aggregate, have a Material Adverse Effect taken as a whole.

     4.9   Valid Issuance Of Shares.  When issued, sold and delivered in
           ------------------------
accordance with the terms hereof for the consideration expressed herein, the
Shares will be duly and validly authorized and issued, fully paid and
nonassessable and, based in part upon the representations of Aventis in Section
6.3 of this Agreement, will be issued in compliance with all applicable federal
and state securities laws.

     4.10  Governmental Consents.  No consent, approval, order or authorization
           ---------------------
of, or registration, qualification, designation, declaration or filing with, any
federal, state or local governmental authority on the part of ViroPharma is
required in connection with the consummation of the transactions contemplated by
the Transaction Documents, except for notices required or permitted to be filed
with certain state and federal securities commissions, which notices will be
filed on a timely basis.

     4.11  No Brokers.  Other than Lazard Freres & Co. LLC which will be the
           ----------
sole obligation of ViroPharma, no broker, finder or investment banker is
entitled to any brokerage,

                                       7
<PAGE>

finder's or other fee or commission in connection with the transactions
contemplated by this Agreement based on arrangements made by ViroPharma.

     4.12  Delaware Law.  To the extent that Aventis shall be deemed to be an
           --------------
"interested stockholder" as defined in Section 203 of the Delaware General
Corporation Law (the "DGCL") solely as a result of the transactions contemplated
by this Agreement, ViroPharma has taken all action necessary to ensure that the
provisions of Section 203 of the DGCL will not be applicable to Aventis or its
Affiliates.

     4.13  Intellectual Property.  As of  August 31, 2001, the Intellectual
           ---------------------
Property that is owned by ViroPharma is owned free from any material liens or
restrictions (except as otherwise set forth in an Intellectual Property License
in respect of such Intellectual Property), and all material Intellectual
Property Licenses are in full force and effect in accordance with their terms,
and are free and clear of any material liens or restrictions, except (a) where
the failure to be free from such liens or restrictions would not have a Material
Adverse Effect, taken as a whole, or (b) as set forth in such Intellectual
Property License. As of August 31, 2001, to the Knowledge of ViroPharma, the
conduct of the business of ViroPharma, as now conducted and proposed to be
conducted under the Copromotion and Codevelopment Agreement does not infringe or
conflict with the rights of any third party in respect of any Intellectual
Property, and none of the Company Intellectual Property is being infringed by
any third party. As of August 31, 2001, there is no claim or demand of any
person or entity pertaining to, or any proceeding which is pending or, to the
Knowledge of ViroPharma, threatened, that challenges the rights of ViroPharma in
respect of any Company Intellectual Property, or that claims that any default
exists under any Intellectual Property License, except where such claim, demand
or proceeding would not materially affect the ability of ViroPharma to conduct
its business as presently conducted or proposed to be conducted under the
Copromotion and Codevelopment Agreement. For purposes of this Agreement,
"Company Intellectual Property" means the Intellectual Property that is owned by
ViroPharma and the Intellectual Property subject to an Intellectual Property
License pursuant to which its use by ViroPharma is permitted by any third party.

5.   Representations And Warranties Of Aventis.  Aventis hereby represents and
     -----------------------------------------
warrants to ViroPharma as of the date hereof and as of the Closing Date as
follows:

     5.1  Legal Power.  Aventis has the requisite corporate power to enter into
          -----------
the Transaction Documents, to carry out and perform its obligations under the
terms of the Transaction Documents.

     5.2  Due Execution.  The Transaction Documents have been duly authorized,
          -------------
executed and delivered by Aventis, and, upon due execution and delivery by
ViroPharma, each of the Transaction Documents will be a valid and binding
agreement of Aventis, except as enforceability may be limited by bankruptcy,
insolvency, reorganization, moratorium or similar laws affecting creditors'
rights generally or by equitable principles.

     5.3  Ownership.  As of the date hereof, Aventis and its Affiliates do not
          ---------
currently own greater than one percent (1%) of the outstanding Voting Stock of
ViroPharma.

                                       8
<PAGE>

     5.4  Investment Representations.  In connection with the offer, purchase
          --------------------------
and sale of the Shares, Aventis makes the following representations:

          (a)  Aventis is acquiring the Shares for its own account, not as
nominee or agent, for investment and not with a view to, or for resale in
connection with, any distribution or public offering thereof within the meaning
of the Securities Act.

          (b)  Aventis understands that:

               (i)     the Shares have not been registered under the Securities
Act by reason of a specific exemption therefrom, that such securities may be
required to be held by it indefinitely under applicable securities laws, and
that Aventis must, therefore, bear the economic risk of such investment
indefinitely, unless a subsequent disposition thereof is registered under the
Securities Act or is exempt from such registration;

               (ii)    each certificate representing such Shares will be
endorsed with the following legend:

"THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
ACT OF 1933, AS AMENDED (THE "ACT"), OR UNDER THE SECURITIES LAWS OF CERTAIN
STATES. THESE SECURITIES ARE SUBJECT TO RESTRICTIONS ON TRANSFERABILITY AND
RESALE AND MAY NOT BE TRANSFERRED OR RESOLD EXCEPT AS PERMITTED UNDER THE ACT
AND ANY APPLICABLE STATE SECURITIES LAWS, PURSUANT TO REGISTRATION OR EXEMPTION
THEREFROM OR UNLESS THE COMPANY HAS RECEIVED AN OPINION OF COUNSEL SATISFACTORY
TO THE COMPANY AND ITS COUNSEL THAT SUCH REGISTRATION IS NOT REQUIRED."; and

               (iii)   ViroPharma will instruct its transfer agent not to
register the transfer of the Shares (or any portion thereof) unless the
conditions specified in the foregoing legends are satisfied.

         (c)   Aventis has such knowledge and experience in financial or
business matters that it is capable of evaluating the merits and risks of the
investment in the Shares to be purchased hereunder.

         (d)   Aventis is an "accredited investor" as such term is defined in
Rule 501(a) of the rules and regulations promulgated under the Securities Act.

6.   Conditions To Closing.
     ---------------------

     6.1  Conditions to Obligations of Aventis at the Closing.  Aventis's
          ---------------------------------------------------
obligation to purchase the Shares at the Closing is subject to the fulfillment
to its reasonable satisfaction, on or prior to the Closing, of all of the
following conditions, any of which may be waived by Aventis:

                                       9
<PAGE>

          (a)  Representations and Warranties True.  The representations and
               -----------------------------------
warranties made by ViroPharma in Section 4 hereof shall be true and correct in
all material respects on the date of this Agreement and (except for those
representations and warranties that address matters as of a particular date
which only need be true and correct as of such date) the Closing Date with the
same force and effect as if they had been made on and as of said date, and a
certificate duly executed by an officer of ViroPharma, to the effect of the
foregoing, shall be delivered to Aventis.

          (b)  Performance of Obligations.  ViroPharma shall have performed and
               --------------------------
complied with all obligations and conditions herein required to be performed or
complied with by it on or prior to the Closing and a certificate duly executed
by an officer of ViroPharma, to the effect of the foregoing, shall be delivered
to Aventis.

          (c)  Proceedings and Documents.  All corporate and other proceedings
               -------------------------
in connection with the transactions contemplated at the Closing and all
documents and instruments incident to such transactions shall be reasonably
satisfactory in substance and form to Aventis, and Aventis shall have received
all such counterpart originals or certified or other copies of such documents as
it may reasonably request.

          (d)  Qualifications; Legal Investment.  All authorizations, approvals,
               --------------------------------
or permits, if any, of any governmental authority or regulatory body of the
United States or of any state that are required in connection with the lawful
sale and issuance of the Shares shall have been duly obtained and shall be
effective on and as of the Closing. No stop order or other order enjoining the
sale of the Shares shall have been issued and no proceedings for such purpose
shall be pending or, to the Knowledge of ViroPharma, threatened by the SEC.

          (e)  Nasdaq Listing.  If required by Nasdaq, the Shares shall have
               --------------
been approved for listing on the Nasdaq Stock Market, subject only to official
notice of issuance. In addition, ViroPharma's Common Stock shall be listed for
trading on the Nasdaq National Market or other national securities exchange or
automated quotation system.

     6.2  Conditions to Obligations of ViroPharma at the Closing.  ViroPharma's
          ------------------------------------------------------
obligation to issue and sell the Shares at the Closing is subject to the
fulfillment to its reasonable satisfaction, on or prior to the Closing, of the
following conditions, any of which may be waived by ViroPharma:

          (a)  Representations and Warranties True.  The representations and
               -----------------------------------
warranties made by Aventis in Section 5 hereof shall be true and correct in all
material respects on the Closing Date with the same force and effect as if they
had been made on and as of said date, and a certificate duly executed by an
officer of Aventis, to the effect of the foregoing, shall be delivered to
ViroPharma.

          (b) Performance of Obligations.  Aventis shall have performed and
              --------------------------
complied with all agreements and conditions herein required to be performed or
complied with by it on or before the Closing, and a certificate duly executed by
an officer of Aventis, to the effect of the foregoing, shall be delivered to
ViroPharma.

                                       10
<PAGE>

          (c)  Qualifications; Legal Investment.  All authorizations, approvals,
               --------------------------------
or permits, if any, of any governmental authority or regulatory body of the
United States or of any state that are required in connection with the lawful
sale and issuance of the Shares shall have been duly obtained and shall be
effective on and as of the Closing. No stop order or other order enjoining the
sale of the Shares shall have been issued and no proceedings for such purpose
shall be pending or, to the Knowledge of ViroPharma, threatened by the SEC.

     6.3  Condition to Obligations of each Party at the Closing.  The
          -----------------------------------------------------
obligations of ViroPharma and Aventis to consummate the transactions
contemplated to occur at the Closing shall be subject to the satisfaction prior
to Closing of the following conditions, each of which may be waived by the other
party only if it is legally permitted to do so.

          (a)  HSR and Other Approvals.  Any applicable waiting period under the
               -----------------------
HSR Act relating to the transactions contemplated hereby shall have expired or
been terminated, and all other material authorizations, consents, orders or
approvals of, or regulations, declarations or filings with, or expirations of
applicable waiting periods imposed by, any Governmental Entity (including,
without limitation, any foreign antitrust filing) necessary for the consummation
of the transactions contemplated hereby, shall have been obtained or filed or
shall have occurred.

          (b)  No Litigation, Injunctions or Restraints.  No statute, rule,
               ----------------------------------------
regulation, executive order, decree, temporary restraining order, preliminary or
permanent injunction or other order enacted, entered, promulgated, enforced or
issued by any governmental entity or other legal restraint or prohibition
preventing the consummation of the transactions contemplated by this Agreement
and the Registration Rights Agreement shall be in effect.

          (c)  Copromotion and Codevelopment Agreement.  The Copromotion and
               ---------------------------------------
Codevelopment Agreement shall continue to be in full force and effect.

          (d)  Triggering Event.  The Triggering Event shall have occurred.
               -----------------

7.   Registration Rights.
     -------------------

     7.1  Piggyback Registrations. ViroPharma shall notify all Holders of
          -----------------------
Registrable Securities in writing at least thirty (30) days prior to the filing
of any Registration Statement (the "Registration Notice"), other than an
Excluded Registration Statement, under the Securities Act for purposes of a
public offering of Common Stock of ViroPharma (including, but not limited to,
Registration Statements relating to secondary offerings of Common Stock of
ViroPharma), and will afford each such Holder an opportunity to include in such
Registration Statement (other than an Excluded Registration Statement) all or
part of such Registrable Securities held by such Holder. Each Holder desiring to
include in any such Registration Statement all or any part of the Registrable
Securities held by it shall, within twenty (20) days after receiving the
Registration Notice from ViroPharma, so notify ViroPharma in writing. Such
notice shall state the intended method of disposition of the Registrable
Securities by such Holder. If a Holder does not elect to include all of its
Registrable Securities in any Registration Statement thereafter filed by
ViroPharma, such Holder shall nevertheless continue to have the right to include
any Registrable

                                       11
<PAGE>

Securities in any subsequent Registration Statement or Registration Statements
as may be filed by ViroPharma with respect to offerings of its securities (other
than an Excluded Registration Statement), all upon the terms and conditions set
forth herein.

          (a)  Underwriting.  If the Registration Statement under which
               ------------
ViroPharma gives notice under this Section 7.1 is for an underwritten offering,
ViroPharma shall so advise the Holders of Registrable Securities. In such event,
the right of any such Holder to be included in a registration pursuant to this
Section 7.1 shall be conditioned upon such Holder's participation in such
underwriting and the inclusion of such Holder's Registrable Securities in the
underwriting to the extent provided herein. All Holders proposing to distribute
their Registrable Securities through such underwriting shall enter into an
underwriting agreement in customary form, reasonably acceptable to such Holder,
with the underwriter or underwriters selected for such underwriting by
ViroPharma, including the indemnification provisions thereof. Notwithstanding
any other provision of the Agreement, if the underwriter determines in good
faith that marketing factors require a limitation of the total number of shares
to be underwritten, ViroPharma and its underwriters shall allocate the number of
Registrable Securities requested to be registered by each of the Holders as
follows: (i) first, to ViroPharma; and (ii) second, to the Holders of
Registrable Securities that have elected to participate in such offering and
such other holders of ViroPharma's capital stock who have been granted
"piggyback" registration rights prior to the date hereof and who have elected to
participate in such offering on a pro rata basis. The Holders of Registrable
Securities acknowledge that the number of securities which may be registered
pursuant to this Section 7 may be reduced to zero. ViroPharma shall have no
obligation under this Section 7 to make any offering of its securities, or to
complete an offering of its securities that it proposes to make, and shall incur
no liability to any Holder for its failure to do so.

          (b)  Right To Terminate Registration.  ViroPharma shall have the right
               -------------------------------
to terminate or withdraw any registration initiated by it under this Section 7.1
prior to the effectiveness of such registration whether or not any Holder has
elected to include securities in such registration, provided that any such
termination or withdrawal shall not relieve ViroPharma of its obligation to pay
for the Registration Expenses incurred and shall be without prejudice to the
Holder's rights under this Section 7 to include such securities in a future
Registration Statement.

     7.2  Expenses Of Registration.  Except as specifically provided herein, all
          ------------------------
Registration Expenses incurred in connection with any registration,
qualification or compliance pursuant to Section 7.1 shall be borne by
ViroPharma, and Selling Expenses incurred in connection with any registration
hereunder shall be borne by the Holders of the securities so registered pro rata
on the basis of the number of securities so registered.

     7.3  Obligations Of ViroPharma.  The obligations of ViroPharma to effect
          -------------------------
the registration of any Registrable Securities pursuant to this Section 7 shall
at all times be subject to the restrictions set forth in Section 8.1. Whenever
required to effect such a registration, ViroPharma shall, as expeditiously as
reasonably possible:

                                       12
<PAGE>

          (a)  Prepare and file with the SEC the requisite registration
statement to effect such registration (including such audited financial
statements as may be required by the Securities Act or the rules and regulations
promulgated thereunder) and thereafter use its reasonable efforts to cause such
registration statement to become and remain effective for a period of time
sufficient to permit distribution of the Registrable Securities as provided in
such Registration Statement.

          (b)  Prepare and file with the SEC such amendments, post-effective
amendments and supplements to such Registration Statement and the prospectus
used in connection therewith as may be necessary to keep such Registration
Statement effective and to comply with the provisions of the Securities Act with
respect to the disposition of all securities covered by such Registration
Statement.

          (c)  Furnish to each Holder of Registrable Securities covered by such
Registration Statement and each underwriter, if any, of the securities being
sold by such Holder such number of conformed copies of such Registration
Statement and of each amendment and supplement thereto (in each case including
all exhibits to such Registration Statement), such number of copies of the
prospectus contained in such Registration Statement (including each preliminary
prospectus and any summary prospectus) and any prospectus filed pursuant to Rule
424 under the Securities Act and such other documents, as such Holder and
underwriter, if any, may reasonably request in order to facilitate the public
sale or other disposition of the Registrable Securities owned by such Holder (it
being understood that ViroPharma consents to the use of the prospectus and any
amendments or supplement thereto by each Holder of Registrable Securities
covered by the Registration Statement and the underwriter or underwriters, if
any, in connection with the offering and sale of Registrable Securities covered
by the prospectus or any amendment or supplement thereto).

          (d)  Use its reasonable efforts to register or qualify all Registrable
Securities under the securities laws or blue sky laws of the jurisdictions as
any Holder thereof and any underwriter of the securities being sold by such
Holder shall reasonably request, to keep such registrations or qualifications in
effect for so long as such registration statement remains in effect, and take
any other action which may be reasonably necessary or advisable to enable such
Holder and underwriter to consummate the disposition in such jurisdictions of
the securities owned by such Holder, except that ViroPharma shall not for any
such purpose be required to qualify generally to do business as a foreign
corporation or become subject to taxation in any jurisdiction wherein it would
not, but for the requirements of this subsection (d), be obligated to be so
qualified, or subject to consent to general service of process in any such
jurisdiction.

          (e)  In the event of any underwritten public offering, enter into and
perform its obligations under an underwriting agreement, in usual and customary
form, with the managing underwriter(s) of such offering. Each Holder
participating in such underwriting shall also enter into and perform its
obligations under such an agreement. In addition, ViroPharma shall, upon the
request of the managing underwriter, make available appropriate ViroPharma
management to participate in customary selling efforts or "road shows," as
appropriate.

                                       13
<PAGE>

          (f)  ViroPharma will notify each Holder of Registrable Securities
covered by such Registration Statement at any time when a prospectus relating
thereto is required to be delivered under the Securities Act, upon ViroPharma's
discovery that, or upon the happening of any event as a result of which the
prospectus included in such registration statement, as then in effect, includes
an untrue statement of a material fact or omits to state any material fact
required to be stated therein or necessary to make the statements therein not
misleading in the light of the circumstances under which they were made, and at
the request of such Holder promptly prepare and furnish to such Holder and each
underwriter, in any, a reasonable number of copies of a supplement to or an
amendment of such prospectus as may be necessary so that, as thereafter
delivered to the purchasers of such securities, such prospectus shall not
include an untrue statement of a material fact or omit to state a material fact
required to be stated therein or necessary to make the statements therein not
misleading in the light of the circumstances then existing.

          (g)  Furnish, at the request of the Holders participating in the
registration, on the date that such Registrable Securities are delivered to the
underwriters for sale: (i) an opinion, dated as of such date, of the counsel
representing ViroPharma for the purposes of such registration, in form and
substance as is customarily given to underwriters in an underwritten public
offering, addressed to the underwriters, and (ii) a letter dated as of such
date, from the independent certified public accountants of ViroPharma, in form
and substance as is customarily given by independent certified public
accountants to underwriters in an underwritten public offering, addressed to the
underwriters.

          (h)  ViroPharma will cause all Registrable Securities covered by the
Registration Statement to be listed on each securities exchange or traded or
quoted on each market on which the same class of securities issued by ViroPharma
are then listed, traded or quoted.

          (i)  ViroPharma will provide a transfer agent and a CUSIP number for
all Registrable Securities no later than the effective date of such Registration
Statement.

     7.4  Delay Of Registration; Furnishing Information.
          ---------------------------------------------

          (a)  No Holder shall have any right to obtain or seek an injunction
restraining or otherwise delaying any such registration as the result of any
controversy that might arise with respect to the interpretation or
implementation of this Section 7.

          (b)  It shall be a condition precedent to the obligations of
ViroPharma to take any action pursuant to Section 7.1 that the selling Holders
shall furnish to ViroPharma such information regarding themselves, the
Registrable Securities held by them and the intended method of disposition of
such securities as shall be legally required under the Securities Act to effect
the registration of their Registrable Securities.

     7.5  Indemnification; Contribution
          -----------------------------

                                       14
<PAGE>

          (a)  ViroPharma shall indemnify and hold harmless each Holder
(including the employees, officers and directors of Aventis) from and against
any and all losses, claims, damages, liabilities and expenses (including
reasonable costs of investigation) arising out of or based upon any untrue, or
allegedly untrue, statement of a material fact contained in any Registration
Statement, prospectus or preliminary prospectus or notification or offering
circular (as amended or supplemented if ViroPharma shall have furnished any
amendments or supplements thereto) or arising out of or based upon any omission
or alleged omission to state therein a material fact required to be stated
therein or necessary to make the statements therein not misleading, except
insofar as the same are caused by or contained in any information concerning
such Holder furnished in writing to ViroPharma by such Holder expressly for use
in such Registration Statement.

          (b)  Each Holder shall indemnify and hold harmless ViroPharma, any
underwriter retained by ViroPharma and their respective directors, officers,
employees and each Person who controls ViroPharma or such underwriter (within
the meaning of the Securities Act and the Exchange Act) from and against any and
all losses, claims, damages, liabilities and expenses (including reasonable
costs of investigation) arising out of or based upon any untrue, or allegedly
untrue, statement of a material fact contained in any Registration Statement,
prospectus or preliminary prospectus or notification or offering circular (as
amended or supplemented if ViroPharma shall have furnished any amendments or
supplements thereto) or arising out of or based upon any omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make the statements therein not misleading, if such statement or
omission was made in reliance upon and in conformity with any information
concerning such Holder furnished in writing to ViroPharma by such Holder
specifically for use in the preparation of such Registration Statement or
prospectus; provided, however, that the total amount to be indemnified by such
            --------  -------
Holder pursuant to this Section 7.5(b) shall be limited to the net proceeds
received by the Holders in the offering to which the Registration Statement or
prospectus relates.

          (c)  Each Person entitled to indemnification hereunder (the
"Indemnified Party") agrees to give prompt written notice to the indemnifying
party (the "Indemnifying Party") after the receipt by the Indemnified Party of
any written notice of the commencement of any action, suit, proceeding or
investigation or threat thereof made in writing for which the Indemnified Party
intends to claim indemnification or contribution pursuant to this Agreement;
provided, however, that the failure to so notify the Indemnifying Party shall
--------  -------
not relieve the Indemnifying Party of any liability that it may have to the
Indemnified Party hereunder unless, and only to the extent that, such failure
results in the Indemnifying Party's forfeiture of substantive rights or
defenses. If notice of commencement of any such action is given to the
Indemnifying Party as above provided, the Indemnifying Party shall be entitled
to participate in and, to the extent it may wish, jointly with any other
Indemnifying Party similarly notified, to assume the defense of such action at
its own expense, with counsel chosen by it and reasonably satisfactory to such
Indemnified Party. The Indemnified Party shall have the right to employ separate
counsel in any such action and participate in the defense thereof, but the fees
and expenses of such counsel (other than reasonable costs of investigation)
shall be paid by the Indemnified Party unless (i) the Indemnifying Party agrees
to pay the same, (ii) the Indemnifying Party fails to assume the defense of such
action with counsel reasonably satisfactory to the Indemnified Party in its
reasonable judgment or (iii) the named parties to any such action

                                       15
<PAGE>

(including any impleaded parties) have been advised by such counsel that either
(x) representation of such Indemnified Party and the Indemnifying Party by the
same counsel would be inappropriate under applicable standards of professional
conduct or (y) there may be one or more legal defenses available to it which are
different from or additional to those available to the Indemnifying Party. In
either of such cases, the Indemnifying Party shall not have the right to assume
the defense of such action on behalf of such Indemnified Party. No Indemnifying
Party shall be liable for any settlement entered into without its written
consent (other than in the case where the Indemnifying Party is unconditionally
released from liability and its rights are not adversely effected), which
consent shall not be unreasonably withheld.

          (d)  If the indemnification provided for in this Section 7.5 from the
Indemnifying Party pursuant to applicable law is unavailable to an Indemnified
Party hereunder in respect of any losses, claims, damages, liabilities or
expenses referred to therein, then the Indemnifying Party, in lieu of
indemnifying such Indemnified Party, shall contribute to the amount paid or
payable by such Indemnified Party as a result of such losses, claims, damages,
liabilities or expenses in such proportion as is appropriate to reflect the
relative fault of the Indemnifying Party and Indemnified Party in connection
with the actions which resulted in such losses, claims, damages, liabilities or
expenses, as well as any other relevant equitable considerations. The relative
faults of such Indemnifying Party and Indemnified Party shall be determined by
reference to, among other things, whether any action in question, including any
untrue or alleged untrue statement of a material fact or omission or alleged
omission to state a material fact, has been made by, or relates to information
supplied by, such Indemnifying Party or Indemnified Party, and the parties'
relative intent, knowledge, access to information and opportunity to correct or
prevent such action. The amount paid or payable by a party as a result of the
losses, claims, damages, liabilities and expenses referred to above shall be
deemed to include, subject to the limitations set forth in Sections 7.5(a), (b)
and (c), any legal or other fees, charges or expenses reasonably incurred by
such party in connection with any investigation or proceeding. The parties
hereto agree that it would not be just and equitable if contribution pursuant to
this Section 7.5(d) were determined by pro rata allocation or by any other
method of allocation which does not take account of the equitable considerations
referred to in the immediately preceding paragraph. No Person guilty of
fraudulent misrepresentation (within the meaning of Section 11(f) of the
Securities Act) shall be entitled to contribution from any Person.

     7.6  Assignment Of Registration Rights.  The rights to cause ViroPharma to
          ---------------------------------
register Registrable Securities pursuant to this Section 7 may only be assigned
by Aventis to a transferee or assignee of Registrable Securities that is an
Affiliate or a successor (by operation of law or otherwise) to substantially all
the business or assets of Aventis; provided, however (i) Aventis shall, within
ten (10) days after such transfer, furnish to ViroPharma written notice of the
name and address of such transferee or assignee and the securities with respect
to which such registration rights are being assigned, and (ii) such transferee
shall agree to be subject to all restrictions with respect to the Shares set
forth in this Agreement.

     7.7  "Market Stand-Off" Agreement.  If requested by ViroPharma or the
          ----------------------------
representative of the underwriters of Common Stock (or other securities) of
ViroPharma, each Holder shall agree not to sell or otherwise transfer or dispose
of any Common Stock (or other securities) of ViroPharma held by such Holder
(other than those included in the registration, if

                                       16
<PAGE>

any) for a period commencing on the date that such Holder receives the
Registration Notice (but in no case earlier than thirty (30) days prior to the
date of the filing of the applicable Registration Statement) and continuing for
the period specified by the representative of the underwriters not to exceed
ninety (90) days following the effective date of a Registration Statement of
ViroPharma filed under the Securities Act, provided that all executive officers
and directors of ViroPharma enter into similar agreements. Notwithstanding the
foregoing, Aventis shall have no obligations under this Section 7.7: (a) in
respect of a private placement by Aventis of any Common Stock (or other
securities) of ViroPharma to the extent that such private placement occurs prior
to the filing of the applicable Registration Statement, (b) from and after the
date that Aventis's registration rights granted hereunder have terminated in
their entirety, or (c) if fifty percent (50%) or more of Common Stock requested
by such Holder to be included in such registration is excluded under Section
7.1(a).

     7.8  Termination Of Registration Rights.  This Section 7 and the
          ----------------------------------
registration rights granted hereunder in respect of the Shares shall terminate
in their entirety on the later of (i) five (5) years from the Closing Date, or
(ii) three (3) months after the Holder ceases to be an "affiliate" (within the
meaning of the Exchange Act or Securities Act) of ViroPharma.

8.   Covenants
     ---------

     8.1  Covenant Of Aventis.  Aventis hereby covenants and agrees that it
          -------------------
shall not exercise the registration rights described in Section 7 during the one
(1) year period following the Closing Date.

     8.2  Covenant Of ViroPharma.
          ----------------------

          (a)  ViroPharma hereby covenants and agrees that it shall take all
necessary and appropriate actions to ensure that it shall have available under
its Restated Certificate of Incorporation as in effect on the Closing Date
sufficient authorized but unissued shares of its Common Stock to issue and sell
to Aventis all of the Shares.

          (b)  ViroPharma will file with Nasdaq all documentation required by
Nasdaq, if any, in connection with the issuance of the Shares.

     8.3  Rights Agreement.  In the event that the purchase of the Shares
          ----------------
hereunder by Aventis at any Closing would cause Aventis to become an "Acquiring
Person," as such term is defined in the Rights Agreement, because either (a) the
Shares, by themselves, constitute in excess of twenty percent (20%) of then-
outstanding Common Stock of ViroPharma (the "Threshold"), or (b) after the date
hereof but prior to the Closing Date Aventis acquires a third party that owns
capital stock of ViroPharma and whose ownership of capital stock of ViroPharma
is not the primary business purpose of such third party (the "Third Party
ViroPharma Stock"), and when the Shares are added together with Third Party
ViroPharma Stock, Aventis's aggregate beneficial ownership exceeds the
Threshold, then prior to the consummation of the Closing, ViroPharma shall cause
the Rights Agreement to be amended to ensure that the acquisition of the Shares
at such Closing does not cause Aventis to become an

                                       17
<PAGE>

Acquiring Person. Notwithstanding the foregoing, nothing in this Section 8.3
shall require ViroPharma to amend the Rights Agreement if Aventis's purchase of
the Shares would result in Aventis becoming an Acquiring Person because such
Shares, when added to any shares of the capital stock of ViroPharma acquired by
Aventis other than under this Agreement or as specifically described in clause
(b) of this Section 8.3, causes Aventis's ownership to exceed the Threshold.

     8.4  Notice of Market Sale.  Aventis shall provide ViroPharma with a notice
          ---------------------
of its intent to sell the Shares pursuant to Rule 144 prior to completing such a
sale in order to provide ViroPharma an opportunity to arrange an orderly
disposition of the Shares. At any point during such thirty (30) day period,
ViroPharma may terminate the remainder of such period and notify Aventis that
Aventis may sell the Shares pursuant to Rule 144. Notwithstanding the foregoing,
Aventis shall have no obligations under this Section 8.4 in respect of a private
placement by Aventis of the Shares.

9    Termination.
     -----------

     9.1  Termination.  This Agreement may be terminated at any time prior to
          -----------
the Closing:

          (a)  by mutual written consent of Aventis and ViroPharma;

          (b)  by Aventis or ViroPharma:

               (i)     if the Closing shall not have occurred prior to the
expiration of the one hundred fifteen (115) day period following the date of the
Triggering Event; provided that the right to terminate this Agreement pursuant
to this clause shall not be available to a party whose failure to fulfill an
obligation under this Agreement results in the failure of the Closing to occur;

               (ii)    if there shall be any statute, law, regulation or rule
that makes consummating the transactions contemplated hereby illegal or if any
court or other Governmental Entity of competent jurisdiction shall have issued
judgment, order, decree or ruling, or shall have taken such other action
restraining, enjoining or otherwise prohibiting the consummation of the
transactions contemplated hereby and such judgment, order, decree or ruling
shall have become final and non-appealable;

               (iii)   if the Copromotion and Codevelopment Agreement shall have
terminated; or

               (iv)    the United States Federal Trade Commission ("FTC") and/or
the United States Department of Justice shall seek a preliminary injunction
under the HSR Act against ViroPharma and Aventis to enjoin the transactions
contemplated by this Agreement or the Copromotion and Codevelopment Agreement;
or

          (c)  by Aventis:

                                       18
<PAGE>

               (i)     if ViroPharma shall have (A) failed to perform any of its
material obligations contained herein, or (B) breached any of its material
representations or warranties contained herein, provided that Aventis gives
ViroPharma written notice of such failure to perform or breach and ViroPharma
does not cure such failure to perform or breach within thirty (30) days after
its receipt of such written notice;

               (ii)    if any of the conditions set forth in Section 6.1 or 6.3
(other than 6.3(a)) shall become impossible to fulfill (other than as a result
of any breach by Aventis of the terms of this Agreement) and shall not have been
waived in accordance with the terms of this Agreement; or

               (iii)   if the Common Stock shall no longer be listed for trading
on the Nasdaq National Market or other national securities exchange or automated
quotation system; provided however, that Aventis may not terminate this
Agreement pursuant to this Section 8.1(c)(iii): (A) prior to the date of the
Triggering Event; and (B) on or after the date of the Triggering Event, if
ViroPharma shall become listed for trading on the Nasdaq National Market or
other national securities exchange or automated quotation system at any time
during the ninety (90) day period after the date of the Triggering Event.

          (d)  by ViroPharma:

               (i)     if Aventis shall have (A) failed to perform any of its
material obligations contained herein, or (B) breached any of its material
representations or warranties contained herein, provided that ViroPharma gives
Aventis written notice of such failure to perform or breach and Aventis does not
cure such failure to perform or breach within thirty (30) days after its receipt
of such written notice; or

               (ii)    if any of the conditions set forth in Section 6.2 or 6.3
shall become impossible to fulfill (other than as a result of any breach by
ViroPharma of the terms of this Agreement) and shall not have been waived in
accordance with the terms of this Agreement.

     9.2  Effect of Termination.  In the event of termination of this Agreement
          ---------------------
by either Aventis or ViroPharma as provided in Section 9.1, this Agreement shall
forthwith become void and have no effect, without any liability or obligation on
the part of Aventis or ViroPharma, other than the provisions of this Section
9.2, and except to the extent that such termination results from a material
breach by a party of its representations, warranties, covenants or agreements
set forth in this Agreement.

10.  Miscellaneous.
     -------------

     10.1  Governing Law.  This Agreement shall be governed by and construed in
           -------------
accordance with the laws of the Commonwealth of Pennsylvania, without regard to
the choice of law provisions thereof, and the federal laws of the United States.

     10.2  Public Statements.  Any statement to the public regarding this
           -----------------
Agreement shall be approved in advance by ViroPharma and Aventis, except as
otherwise required by law.

                                       19
<PAGE>

Notwithstanding the foregoing, Aventis acknowledges that ViroPharma shall file
this Agreement with the SEC.

     10.3  Successors And Assigns.  Except as otherwise expressly provided
           ----------------------
herein, the respective rights and obligations of either Party under this
Agreement shall not be assignable in whole or in part by a Party without the
prior written consent of the other Party, which consent shall not be
unreasonably withheld or delayed. Notwithstanding the preceding sentence, in
connection with the merger, acquisition, transfer of all or substantially all of
a Party's assets or other change in control of either Party, such Party may
assign its rights and obligations under this Agreement in whole or in part to
such Party's transferee or successor in interest without the prior written
consent of the other Party. This Agreement shall bind and inure to the benefit
of Parties and their permitted successors and assigns.

     10.4  Entire Agreement.  This Agreement, the Copromotion and Codevelopment
           ----------------
Agreement and the exhibits thereto, that certain Mutual Non-Disclosure Agreement
dated as of March 1, 2001 between the ViroPharma and Aventis and that certain
Letter Agreement dated April 17, 2001 between ViroPharma and Aventis and the
other documents delivered pursuant hereto, constitute the full and entire
understanding and agreement among the Parties with regard to the subjects hereof
and no Party shall be liable or bound to any other Party in any manner by any
representations, warranties, covenants, or agreements except as specifically set
forth herein or therein. Nothing in this Agreement, express or implied, is
intended to confer upon any Party, other than the parties hereto and their
respective successors and assigns, any rights, remedies, obligations, or
liabilities under or by reason of this Agreement, except as expressly provided
herein.

     10.5  Separability.  In the event any provision of this Agreement shall be
           ------------
invalid, illegal, or unenforceable, it shall to the extent practicable, be
modified so as to make it valid, legal and enforceable and to retain as nearly
as practicable the intent of the Parties, and the validity, legality, and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.

     10.6  Amendment And Waiver.  Except as otherwise provided herein, any term
           --------------------
of this Agreement may be amended and the observance of any term of this
Agreement may be waived (either generally or in a particular instance, either
retroactively or prospectively, and either for a specified period of time or
indefinitely), with the written consent of ViroPharma and Aventis. Any amendment
or waiver effected in accordance with this Section shall be binding upon any
holder of any securities purchased under this Agreement (including securities
into which such securities have been converted), each future holder of all such
securities, and ViroPharma.

     10.7  Notices.   All notices, requests, or other communications given
           -------
hereunder shall be in writing and shall be deemed to have been duly given if (a)
delivered by hand; (b) mailed by registered or certified mail; (c) sent by air
courier; or (d) sent by cable, telex or facsimile, followed within twenty-four
(24) hours by notification pursuant to (a), (b) or (c) above, in each case to
the address set forth below or to such other address as a Party may specify for
itself by written notice given as aforesaid.

                                       20
<PAGE>

     If to Aventis:           Pharma Inc.
                              2150 Saint Elzear Blvd. West
                              Laval, Quebec, Canada
                              H7L 4A8
                              FAX:  514-956-4192
               Attention:     Vice-President, Finance and Information Solutions

    with a copy to:           Aventis Pharma Inc.
                              2150 Saint Elzear Blvd. West
                              Laval, Quebec, Canada
                              H7L 4A8
                              FAX: 514-956-6171
                              Attention:     General Counsel

            and to:           Aventis Pharmaceuticals Inc.
                              Route 202-206
                              P.O. Box 6800
                              Bridgewater, NJ 08807, U.S.A.
                              Facsimile: 1-908-231-4480
                              Attention: Vice President, Legal Department

  If to ViroPharma:           ViroPharma Incorporated
                              405 Eagleview Boulevard
                              Exton, PA 19341
                              FAX: 610-458-7380
                              Attention:     Chief Financial Officer

    with a copy to:           ViroPharma Incorporated
                              405 Eagleview Boulevard
                              Exton, PA 19341
                              FAX: 610-458-7380
                              Attention:     General Counsel

     10.8  Fees And Expenses.  ViroPharma and Aventis shall each bear their own
           -----------------
expenses and legal fees incurred on their behalf with respect to this Agreement
and the transactions contemplated hereby.

     10.9  Titles And Subtitles.  The titles of the Sections and subsections of
           --------------------
this Agreement are for convenience of reference only and are not to be
considered in construing this Agreement.

                                       21
<PAGE>

     10.10  Counterparts.  This Agreement may be executed in any number of
            ------------
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one instrument.

                                       22
<PAGE>

IN WITNESS WHEREOF, this Stock Purchase Agreement is hereby executed as of the
date first above written.

                              VIROPHARMA INCORPORATED

                              By:   /s/ Michel de Rosen
                                   ---------------------------------
                                   Michel de Rosen
                                   President and CEO

                              AVENTIS PHARMA INC.

                              By:   /s/ Jean-Francois Leprince
                                   ---------------------------------
                                   Jean-Francois Leprince
                                   President

                                       23
<PAGE>

                  Exhibit 4.1 to the Stock Purchase Agreement

           Exceptions to Capitalization Representation and Warranty
           --------------------------------------------------------

Certain preemptive rights were granted pursuant to that certain Investment
Agreement dated May 5, 1999 between ViroPharma Incorporates and PSV, LP (f/k/a
Perseus-Soros BioPharmaceutical Fund, LP).

Common Stock subject to sale pursuant to that certain Stock Purchase Agreement
dated as of December 9, 1999 between ViroPharma Incorporated and American Home
Products Corporation.

                                       24

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