Document:

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                                                                   Exhibit 10.30

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

                                LICENSE AGREEMENT

                                 by and between

                                  SEPRACOR INC.

                                       and

                          HOECHST MARION ROUSSEL, INC.

                                 August 31, 1999

      This document is the confidential information of both parties hereto.
    It should be distributed on a need-to-know basis and kept in secure area.
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ARTICLE 1 - DEFINITIONS................................................2

ARTICLE 2 - ASSIGNMENT AND LICENSE GRANT...............................6

ARTICLE 3 - ROYALTIES AND OTHER CONSIDERATION..........................7

ARTICLE 4 - ROYALTY PAYMENTS, REPORTS AND RECORDS......................7

ARTICLE 5 - RIGHTS IN TECHNOLOGY, INVENTIONS AND PATENTS..............10

ARTICLE 6 - INFRINGEMENT INVOLVING PRODUCT............................10

ARTICLE 7 - CONFIDENTIALITY...........................................12

ARTICLE 8 - TERM......................................................13

ARTICLE 9 - BREACH AND TERMINATION....................................13

ARTICLE 10 - RIGHTS AND OBLIGATIONS UPON TERMINATION..................14

ARTICLE 11 - REPRESENTATIONS AND WARRANTIES...........................14

ARTICLE 12 - INDEMNIFICATION..........................................16

ARTICLE 13 - CHOICE OF LAW............................................16

ARTICLE 14 - FORCE MAJEURE............................................17

ARTICLE 15 - NOTICES..................................................17

ARTICLE 16 - WAIVER...................................................18

ARTICLE 17 - ENTIRE AGREEMENT.........................................18

ARTICLE 18 - ASSIGNMENT...............................................18

ARTICLE 19 - TITLES...................................................19

ARTICLE 20 - PUBLICITY................................................19

ARTICLE 21 - UNENFORCEABLE PROVISIONS.................................21

ARTICLE 22 - CONSTRUCTION.............................................21

ARTICLE 23 - HMR OWNERSHIP............................................21

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ARTICLE 24 - EXECUTION................................................22

ARTICLE 25 - CLOSING..................................................22

SCHEDULE 1.21     SEPRACOR PATENTS

SCHEDULE 2.1      FORM OF ASSIGNMENT

SCHEDULE 20.1     JOINT PRESS RELEASE

SCHEDULE 20.2.2   LISTING OF ALLEGRA(R)

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          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

This License Agreement is made as of this 31st day of August, 1999 by and
between Sepracor Inc. ("Sepracor"), a Delaware corporation having a place of
business at 111 Locke Drive, Marlborough, Massachusetts 01752, and Hoechst
Marion Roussel, Inc. ("HMR"), a Delaware corporation having a place of business
at Route 202-206, P.O. Box 6800, Bridgewater, New Jersey 08867.

BACKGROUND

WHEREAS, Sepracor is the assignee of U.S. Patent No. 5,375,693, entitled
"Methods and Compositions for Treating Allergic Disorders and Other Disorders
using Metabolic Derivatives of Terfenadine" (the "693 Patent") and U.S. Patent
Application Serial No. 08/191,149, entitled "Methods and Compositions for
Treating Allergic Disorders and Other Disorders using Optically Pure Isomers of
Metabolic Derivatives of Terfenadine" (the "149 Application");

WHEREAS, Sepracor also owns a portfolio of patents and patent applications
generally directed to Terfenadine Carboxylate Technology and certain know-how
relating to the use of Terfenadine Carboxylate Technology;

WHEREAS, the parties entered into a license agreement on June 1, 1993 (the "1993
License Agreement"), whereby Sepracor granted HMR an exclusive license under
U.S. Patent Application Serial No. 07/924,156 entitled "Methods and Compositions
for Treating Allergic Disorders and Other Disorder using Metabolic Derivatives
of Terfenadine" (the "156 Application") and any patents issuing therefrom, and
the 693 Patent subsequently issued from a continuation of the 156 Application;

WHEREAS, HMR made two milestone payments to Sepracor under the 1993 License
Agreement, such payments were made under protest and totaled [**];

WHEREAS, an interference was declared by the U.S. Patent and Trademark Office
("PTO") relating to the 693 Patent, the 149 Application, and HMR's U.S. Patent
Application Serial No. 08/397,542, entitled "A Method of Providing an
Antihistaminic Effect in a Hepatically Impaired Patient" (the "542
Application");

WHEREAS, on the terms and conditions set forth herein, Sepracor is willing to
assign the Assigned Patents (as defined below) to HMR and license to HMR the
exclusive right to use additional Sepracor Patents and Sepracor Know-How to
develop and sell Products; and

WHEREAS, HMR wishes to accept such assignment and license.

NOW, THEREFORE, in consideration of the mutual promises, covenants and
agreements hereinafter set forth, the sufficiency of which is hereby
acknowledged, the parties to this

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          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

Agreement mutually agree as follows:

ARTICLE 1 - DEFINITIONS

For purposes of this Agreement, the following initially capitalized terms in
this Agreement, whether used in the singular or plural, shall have the following
meanings, unless the context clearly requires otherwise:

1.1   Affiliate. "Affiliate" shall mean, with respect to either party hereto,
      any corporation, company, partnership, joint venture or any other entity
      which directly or indirectly controls, is controlled by, or is under
      common control with such party. For purposes of this definition, "control"
      shall mean direct or indirect ownership of at least fifty percent (50%) of
      the outstanding voting securities of the entity.

1.2   Agreement. "Agreement" shall mean this License Agreement, including all
      Schedules hereto.

1.3   Assigned Patents. "Assigned Patents" shall mean U.S. Patent No. 5,375,693,
      U.S. Patent Application Serial No. 08/191,149, and any and all related
      United States patent applications, including any additions, divisions,
      continuations, continuations-in-part, reissues, reexaminations,
      substitutions, extensions, patent term extensions and renewals thereof,
      and patents issued therefrom.

1.4   Business Day. "Business Day" shall mean a day on which banks are open for
      business in both Marlborough, Massachusetts and Bridgewater, New Jersey.

1.5   Closing Date. "Closing Date" shall mean the latest of (a) the date on
      which Sepracor executes this Agreement; (b) the date on which HMR executes
      this Agreement; and (c) if applicable, not later than the fifth Business
      Day following the expiration or earlier termination of any notice and
      waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of
      1976, as amended ("HSR Act").

1.6   Combination Patent. "Combination Patent" shall mean United States Patent
      Application Serial No. [**], and any and all related United States patent
      applications, including any additions, divisions, continuations,
      continuations-in-part, reissues, reexaminations, substitutions,
      extensions, patent term extensions and renewals thereof, and patents
      issued therefrom.

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          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

1.7   Combination Product. "Combination Product" shall mean a Product which is
      comprised in part of Compound, and in part of one or more other active
      ingredients; provided, however, that Combination Product shall not include
      any Product encompassed by a Live Claim of an issued Combination Patent.
      Notwithstanding the foregoing, Products containing Compound and
      pseudoephedrine as the only active ingredients, including but not limited
      to the Product currently identified by the trademark Allegra-D(R), shall
      not be considered a Combination Product for the purposes of this
      Agreement.

1.8   Compound. "Compound" shall mean the terfenadine metabolite known as
      terfenadine carboxylate and fexofenadine, also identified by the chemical
      name 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]-
      (alpha),(alpha)-dimethyl benzeneacetic acid, and any stereoisomer,
      solvate, clathrate, salt, or non-covalent derivative thereof.

1.9   Confidential Information. "Confidential Information" shall mean all
      Sepracor Know-How, and all technical and scientific know-how and
      information, pre-clinical and clinical trial results, computer programs,
      knowledge, technology, means, methods, processes, practices, formulas,
      techniques, procedures, designs, drawings, apparatus, written and oral
      representations of data, specifications, and all other scientific,
      clinical, regulatory, marketing, financial and commercial information or
      data, whether communicated in writing, verbally or electronically, which
      is provided by one party to the other party in connection with this
      Agreement. When Confidential Information is disclosed in a manner other
      than in writing, it shall be reduced to written form, marked
      "Confidential" and transmitted to the receiving party within [**] Business
      Days of disclosure to the receiving party.

1.10  Control or Controlled. "Control" or "Controlled", when used in connection
      with intellectual property rights, shall mean the legal authority or right
      of a party hereto to grant a license or sublicense of intellectual
      property rights to another party hereto, or to otherwise disclose
      proprietary or trade secret information to such other party, without
      breaching the terms of any agreement with a Third Party, or
      misappropriating the proprietary or trade secret information of a Third
      Party. Information that is generally known or available to the public as
      of the Closing Date, or which becomes known or available to the public
      through no fault of the party, shall not be deemed Controlled by a party
      hereto.

1.11  Dollar. "Dollar" shall mean lawful money of the United States of America.

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          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

1.12  Generic Equivalent. "Generic Equivalent" shall mean any pharmaceutical
      product that is sold by a Third Party without the consent or approval of
      HMR or any Affiliate or Licensee thereof, and which includes the same
      Compound as an active ingredient as that used in a particular Product for
      the same indication and by the same route of administration as the
      particular Product. For the purposes of this Section 1.12, an Optically
      Pure stereoisomer of a Compound shall be considered a separate and
      distinct Compound, and solvates, clathrates, salts or noncovalent
      derivatives of a Compound shall be considered one and the same Compound.

1.13  Improvement. "Improvement" shall mean any enhancement of or improvement to
      Terfenadine Carboxylate Technology developed, invented or acquired by, or
      coming under the Control of, Sepracor during the term of this Agreement.

1.14  Licensee. "Licensee" shall mean any person, corporation, unincorporated
      body, or other entity that is not an Affiliate of HMR and to whom HMR
      grants a license or sublicense of the rights assigned or granted to HMR
      pursuant to this Agreement.

1.15  Live Claim. "Live Claim" shall mean a claim of any issued, unexpired
      patent which has not been withdrawn, canceled or surrendered, or held
      invalid or unenforceable by a court of competent jurisdiction in a final,
      unappealable decision.

1.16  Net Sales. "Net Sales" shall mean the gross amount invoiced by HMR and its
      Affiliates and Licensees on account of sales of Product to Third Parties
      in the Territory, less the total of (a) [**] and/or [**] and other [**] to
      the extent [**] in the [**] and other [**] to the extent [**] in the [**]
      by reason of [**] or the equivalents thereof.

      Actual Net Sales for any Combination Product (except Product encompassed
      by a Live Claim of an issued Combination Patent) shall be multiplied by
      the Combination Allocation Portion (as defined below) attributable to such
      Combination Product. The "Combination Allocation Portion", as used herein,
      shall mean [**] only the [**] of the [**] only the [**] and the [**] of
      the [**] that are [**] in Section 1.16(a)-(f) above. [**] for the [**] in
      the [**] that are [**] on the [**]

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1.17  Optically Pure. "Optically Pure" shall mean Compound comprising at least
      ninety percent (90%) by weight of one stereoisomer and ten percent (10%)
      by weight or less of the other stereoisomer.

1.18  Payment Period. "Payment Period" shall mean a calendar quarter ending on
      March 31st, June 30th, September 30th, or December 31st .

1.19  Product. "Product" shall mean any composition which contains Compound as
      an active ingredient. Product shall include any Product encompassed by a
      Live Claim of an issued Combination Patent. Product containing an
      Optically Pure stereoisomer of a Compound shall be considered a separate
      and distinct Product. Product containing solvates, clathrates, salts or
      noncovalent derivatives of a Compound shall be considered one and the same
      Product. If encompassed by a Live Claim of a Combination Patent, Product
      containing one or more leukotriene inhibitors and fexofenadine shall be
      considered a separate and distinct Product, and not a Combination Product.
      Line extensions of a Product shall be considered one and the same Product;
      for example, the composition currently identified by the trademark
      Allegra-D(R) shall be considered the same Product as the composition
      currently identified by the trademark Allegra(R).

1.20  Sepracor Know-How. "Sepracor Know-How" shall mean all proprietary,
      non-public Terfenadine Carboxylate Technology, including, without
      limitation, processes, techniques, formulas, data, methods, equipment
      designs, know-how, show-how and trade secrets, discoveries, practices,
      inventions, technology, manufacturing procedures, test procedures,
      purification and isolation techniques, instructions, test data and other
      intellectual property, patentable or otherwise, tangible or intangible,
      that are owned or Controlled by Sepracor as of the Closing Date or which
      were developed by or at the request of Sepracor prior to or during the
      term of this Agreement and which are not generally known; provided,
      however, that "Sepracor Know-How" shall not include any HMR information or
      materials.

1.21  Sepracor Patents. "Sepracor Patents" shall mean all United States patents
      and patent applications owned or Controlled by Sepracor and relating to
      Terfenadine Carboxylate Technology, including those set forth in Schedule
      1.21 hereto as it may be updated from time to time, and all additions,
      divisions, continuations, continuations-in-part, substitutions,
      extensions, patent term extensions and renewals thereof, and patents
      issued thereon. The term "Sepracor Patents" includes Combination Patents,
      but does not include the Assigned Patents.

1.22  Sepracor Technology. "Sepracor Technology" shall mean the Sepracor
      Patents, Sepracor Know-How and Improvements.

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          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

1.23  Terfenadine Carboxylate Technology. "Terfenadine Carboxylate Technology"
      shall mean technology related to Compound, including, but not limited to,
      methods of use, processes, compositions, or formulations thereof.

1.24  Territory. "Territory" shall mean the United States of America and its
      territories and possessions as of the Closing Date.

1.25  Third Party. "Third Party" shall mean any person, corporation,
      unincorporated body, or other entity other than Sepracor and HMR and their
      respective Affiliates and HMR's Licensees.

ARTICLE 2 - ASSIGNMENT AND LICENSE GRANT

2.1   On the Closing Date, Sepracor shall assign all right, title and interest
      to the Assigned Patents to HMR pursuant to an assignment substantially in
      the form attached hereto as Schedule 2.1. HMR may, at its sole discretion,
      attend to filing and recordation thereof with the U.S. Patent and
      Trademark Office (PTO).

2.2   Sepracor grants to HMR an exclusive license (exclusive even as to
      Sepracor) to develop, have developed, make, have made, use, market, sell,
      have sold and distribute Product in the Territory under the Sepracor
      Technology, subject to the terms and conditions set forth in this
      Agreement.

2.3   The rights and licenses granted hereunder to the Sepracor Patents shall be
      sublicensable by HMR subject to the terms and conditions set forth in this
      Agreement, provided that HMR remains responsible to Sepracor under this
      Agreement and each Licensee confirms in writing to HMR that it agrees to
      be bound by all of the terms and conditions contained in this Agreement.

2.4   To the extent necessary, each of Sepracor and HMR shall file within
      fifteen (15) days after the date of this Agreement with the Federal Trade
      Commission and the Antitrust Division of the U.S. Department of Justice,
      any notification and report form required of it in the reasonable opinion
      of both Parties under the HSR Act with respect to the transactions
      contemplated hereby. The parties shall cooperate with one another to the
      extent necessary in the preparation of any notification and report form
      required to be filed under the HSR Act. Each Party shall be responsible
      for its own costs, expenses, and filing fees associated with any filing
      under the HSR Act.

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          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

ARTICLE 3 - ROYALTIES AND OTHER CONSIDERATION

3.1   In consideration of the assignment of the Assigned Patents and the rights
      and licenses granted under the Sepracor Technology:

      3.1.1 HMR shall pay to Sepracor a royalty of [**] on the Net Sales of
            Product in the Territory ("Royalties");

      3.1.2 Royalties shall be payable on Net Sales of Product in the Territory
            for sales made on or after February 17, 2001, and shall continue on
            a Product by Product basis until the first to occur of the following
            events: (1) with respect to a particular Product line, the
            introduction in the Territory of a Generic Equivalent of a Product
            in such Product line by a Third Party without approval or consent of
            HMR or any Affiliate or Licensee thereof; or (2)(a) with respect to
            all Products (except as provided in clause (2)(b) below), the
            anniversary of the Closing Date in the year 2012, or (b) with
            respect to a Product encompassed by a Live Claim of an issued
            Combination Patent, the expiration date of such Combination Patent.
            Royalties payable for the month of February 2001 shall be calculated
            on a pro rata basis, i.e., twelve twenty-eighths (12/28) of the
            total Net Sales for February 2001 will be used to calculate the
            Royalties due for February 2001. In addition, Royalties payable for
            the month during which Royalties on a Product cease to be payable
            shall also be calculated on a pro rata basis ; and

      3.1.3 Sepracor shall retain the payment of [**] made by HMR to Sepracor on
            April 30, 1997, and the payment of [**] made by HMR to Sepracor on
            May 4, 1998, both payments having been made by HMR to Sepracor in
            connection with Section 4.1 of the 1993 License Agreement and under
            protest, and such payments shall be non-refundable and
            non-creditable.

ARTICLE 4 - ROYALTY PAYMENTS, REPORTS AND RECORDS

4.1   HMR shall deliver to Sepracor within [**] days following the end of each
      Payment Period, beginning with the first Payment Period, a written report
      (the "Royalty Statement") describing, for the applicable Payment Period:

      (a)   the gross sales during the Payment Period for all Products;

      (b)   the Net Sales during the Payment Period for all Products; and

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         Securities and Exchange Commission. Asterisks denote omissions.

      (c)   the calculation used to determine the total Royalties due for the
            Payment Period.

4.2   Each Royalty Statement for a Payment Period required by Section 4.1 above
      shall be accompanied by full payment to Sepracor, made in accordance with
      Section 4.3, of Royalties and any interest that may have accrued in
      accordance with Articles 3 and 4.

4.3   With regard to any payments due to Sepracor, the following shall apply:

      (a)   All payments to Sepracor pursuant to this Agreement shall be made by
            wire transfer, to Fleet Bank of Massachusetts, 75 State Street,
            Boston, Massachusetts 02109 (ABA #011000138) to Account No. [**] or
            such other bank or account as Sepracor may from time to time
            designate in writing. All such payments shall be made in Dollars.

      (b)   Whenever any payment hereunder shall be stated to be due on a day
            which is not a Business Day, such payment shall be made on the
            immediately succeeding Business Day.

      (c)   Payments hereunder shall be considered to be made as of the day on
            which they are received in Sepracor's designated bank account.

      (d)   All payments due to Sepracor hereunder but not paid by HMR on the
            due date thereof shall bear interest at the rate which is the lesser
            of: (i) LIBOR plus two percent (2%) per annum; and (ii) the maximum
            lawful interest rate permitted under applicable law. Such interest
            shall accrue on the balance of unpaid amounts from time to time
            outstanding from the date on which portions of such amounts become
            due and owing until payment thereof in full.

4.4   Any income or other taxes which HMR is required by law to pay or withhold
      on behalf of Sepracor with respect to Royalties, and any interest thereon,
      payable to Sepracor under this Agreement, shall be deducted from the
      amount of such Royalties and interest due, and paid or withheld, as
      appropriate, by HMR on behalf of Sepracor. Any such tax required to be
      paid or withheld shall be an expense of, and borne solely by, Sepracor.
      The previous two sentences notwithstanding, the parties hereto will
      reasonably cooperate in completing and filing documents required under the
      provisions of any applicable tax laws or under any other applicable law,
      in order to enable HMR to make such payments to Sepracor without any
      deduction or withholding.

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4.5   HMR shall keep and maintain, and shall cause its Affiliates and its
      Licensees to keep and maintain, complete and accurate records and books of
      account in sufficient detail and form so as to enable Royalties and any
      interest payable to be determined, including, but not limited to, true and
      accurate records of sales of Products and calculations of Net Sales and
      Royalties. Sepracor shall have the right to audit the records of HMR at
      its own expense (except as otherwise provided in Section 4.6) using HMR's
      independent certified accountants unless good cause can be shown as to why
      such accountants should not be used, in which case Sepracor may elect to
      use any nationally recognized firm of independent certified accountants to
      whom HMR has shown no good cause objection. Such accountants will have
      access on reasonable notice to HMR and its Affiliates' and Licensees'
      records during reasonable business hours for the purpose of verifying the
      Royalties and any interest payable as provided in this Agreement for the
      two preceding years. Notwithstanding the foregoing, this right may not be
      exercised more than once in any calendar year, and once a calendar year is
      audited it may not be reaudited, and said accountant shall disclose to
      Sepracor only information relating solely to the accuracy of the Royalty
      Statements provided to Sepracor and the payments made to Sepracor under
      this Agreement.

4.6   Any adjustment required as a result of an audit conducted under this
      Article shall be made within twenty-five (25) days after the date on
      which the accountant conducting the audit issues a written report to
      Sepracor and HMR containing the results of the audit. If any
      underpayment by HMR is greater than ten percent (10%) of the amount
      previously paid to Sepracor for the relevant Payment Period, the costs
      and expenses of the audit shall be paid for by HMR. In the case of
      overpayment, HMR may elect, at its option, to either offset any
      Royalties and any interest payable to Sepracor by the amount of the
      overpayment or request reimbursement and HMR shall, within [**] Business
      Days of issuance of the auditor's written report, provide written
      notice to Sepracor of its election regarding any overpayment. If HMR
      elects reimbursement of an overpayment, Sepracor shall have the longer
      of a) ten (10) Business Days from its receipt of HMR's written notice, or
      b) ten (10) days after the date on which the accountant conducting the
      audit issues a written report to Sepracor and HMR containing the results
      of the audit, to send HMR the requested overpayment reimbursement.

4.7   No part of any amount payable to Sepracor under this Agreement may be
      reduced due to any counterclaim, set-off, adjustment or other right which
      HMR might have against Sepracor, any other party or otherwise, except as
      expressly stated to the contrary in this Agreement.

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ARTICLE 5 - RIGHTS IN TECHNOLOGY, INVENTIONS AND PATENTS

5.1   Sepracor agrees to use reasonable efforts to continue, at its sole cost
      and expense, the prosecution of the Sepracor Patents and maintenance of
      the Sepracor Patents and Sepracor Know-How. Prosecution of pending patent
      applications shall mean through final patent office appeal and any
      interference proceedings or the like, including, but not limited to,
      re-issue applications and re-examination proceedings.

5.2   After the Closing Date, Sepracor and HMR shall consult with each other in
      connection with the prosecution and maintenance of the Sepracor Patents.
      Sepracor agrees to provide HMR with a reasonable opportunity to comment on
      all material written correspondence with the PTO in connection with
      Sepracor Patents, and Sepracor shall notify HMR of the allowance, grant or
      acceptance of any Sepracor Patent. Should Sepracor decide not to pursue or
      maintain any of the Sepracor Patents, it shall first offer to assign such
      Sepracor Patents to HMR before letting such Sepracor Patents lapse.

5.3   Sepracor shall consult and cooperate with HMR in good faith with respect
      to the filing and prosecution of any patent applications for Improvements
      and the maintenance of patents issued thereon including, without
      limitation, by executing and obtaining from employees and other persons
      all assignments and other documents reasonably required in connection
      therewith.

5.4   The parties agree to cooperate in order to avoid loss of any rights which
      may otherwise be available to the parties under the U.S. Drug Price
      Competition and Patent Term Restoration Act of 1984 and other similar
      measures. Without limiting the foregoing, each of HMR and Sepracor agrees
      to provide the other with reasonable information and assistance in order
      to permit the timely filing of an application for patent term extension
      within the sixty (60) day period following NDA approval to market Product
      in the United States.

ARTICLE 6 - INFRINGEMENT INVOLVING PRODUCT

6.1   In the event that either HMR or Sepracor becomes aware of Third Party
      infringement of any issued Sepracor Patent in the Territory, which
      infringement involves Product, it will notify the other party in writing
      to that effect. Any such notice shall include evidence to support an
      allegation of infringement by such Third Party.

      6.1.1 Except as provided in Section 6.1.3, HMR shall have the right, but
            not the obligation, to enforce (with Sepracor's cooperation and at
            HMR's expense) any Sepracor Patents licensed hereunder against
            infringement by Third Parties. Any recovery or damages derived from
            enforcement of any Sepracor Patent shall be used to first reimburse
            HMR for its documented out-of-pocket legal expenses and costs
            relating to such enforcement, then

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            to reimburse Sepracor for its documented out of pocket legal
            expenses and costs relating to such enforcement. Any remaining
            compensatory damages, such as lost profit damages and reasonable
            royalty damages, shall be treated as Net Sales hereunder for which
            Sepracor shall be entitled to receive a royalty as provided in
            Articles 3 and 4 of this Agreement. Any punitive damages, exemplary
            damages, or other enhanced damages shall be shared equally by the
            parties.

      6.1.2 Except as provided in Section 6.1.3, in the event of infringement of
            Sepracor Patents, if HMR does not file suit or enter into
            negotiations with the Third Party infringer of such Sepracor Patents
            within three (3) months of receiving evidence of such infringement
            that provides a reasonable basis for jurisdiction of a court, then
            Sepracor shall have the right, but not the obligation, to enforce
            the Sepracor Patents against such infringement (on its own behalf
            and at its own expense). Any recovery or damages derived from
            enforcement of any Sepracor Patent shall first be used to reimburse
            Sepracor for its documented out of pocket legal expenses and costs
            relating to such enforcement, then to reimburse HMR for its
            documented out of pocket legal expenses and costs relating to such
            enforcement. Any remaining damages shall be divided by allocating
            three quarters of such damages to Sepracor and one quarter of such
            damages to HMR.

      6.1.3 Notwithstanding any other provisions herein, if HMR, or its
            Affiliates or Licensees is not selling any Product recited in a Live
            Claim of an issued Combination Patent in the Territory, and
            infringement by a Third Party involves Product recited in a Live
            Claim of an issued Combination Patent, Sepracor shall have the
            right, but not the obligation, to enforce the Combination Patents
            against such infringement (on its own behalf and at its own
            expense), and Sepracor shall retain all recoveries from such
            enforcement.

6.2   In any suit or dispute involving infringement of Sepracor Patents or
      Assigned Patents by a Third Party, the parties shall cooperate fully. Upon
      the request and at the expense of the party bringing suit, the other party
      shall make available to the party bringing suit (at reasonable times and
      under appropriate conditions) all relevant assistance. In particular, the
      parties agree to furnish technical and other necessary assistance to each
      other in conducting any litigation necessary to enforce or defend the
      Sepracor Patents and Assigned Patents against Third Parties.

ARTICLE 7 - CONFIDENTIALITY

7.1   During the term of this Agreement, and for a period of five (5) years
      thereafter, each party hereto will maintain in confidence all Confidential
      Information disclosed by the other party hereto. Neither party shall use,
      disclose or grant use of such

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      Confidential Information except as required under this Agreement. To the
      extent that disclosure is authorized by this Agreement, the disclosing
      party shall obtain prior agreement from its employees, agents,
      consultants, Affiliates, Licensees or clinical investigators to whom
      disclosure is to be made to hold in confidence and not make use of such
      information for any purpose other than those permitted by this Agreement.
      Each party shall use at least the same standard of care as it uses to
      protect its own Confidential Information to ensure that such employees,
      agents, consultants, Affiliates, Licensees, and clinical investigators do
      not disclose or make any unauthorized use of such Confidential
      Information. Each party shall promptly notify the other upon discovery of
      any unauthorized use or disclosure of Confidential Information.
      Confidential Information shall not include any information which:

      7.1.1 was already known to the receiving party, other than under an
            obligation of confidentiality, at the time of disclosure by the
            other party;

      7.1.2 was generally available to the public or otherwise part of the
            public domain at the time of its disclosure to the other party;

      7.1.3 becomes generally available to the public or otherwise part of the
            public domain after its disclosure and other than through any act or
            omission of the receiving party in breach of this Agreement;

      7.1.4 was disclosed to the receiving party, other than under an obligation
            of confidentiality, by a Third Party who had no obligation to the
            other party not to disclose such information; or

      7.1.5 was independently developed by the receiving party without reference
            to the disclosure by the other party.

7.2   The parties agree that the material financial terms of the Agreement shall
      be considered the Confidential Information of both parties.

7.3   Each party may disclose the Confidential Information to the extent such
      disclosure is reasonably necessary in filing or prosecuting patent
      applications, prosecuting or defending litigation, or complying with any
      applicable statute or governmental regulation. In addition, either party
      may disclose Confidential Information to its Affiliates, and HMR may
      disclose Confidential Information to Licensees; provided, however, in
      connection with any such disclosure the disclosing party shall use
      diligent efforts to secure confidential treatment of such information.

7.4   The parties shall undertake to ensure that all their employees who have
      access to Confidential Information of the other party are under
      obligations of confidentiality fully consistent with those provided in
      this Article 7.

                                       12
<PAGE>

7.5   To the extent legally required, the parties agree to comply with the
      requirements of 35 U.S.C.ss.135(c) relating to submission of agreements
      between the parties to the U.S. Patent and Trademark Office.

ARTICLE 8 - TERM

8.1   This Agreement will commence as of the Closing Date and, unless sooner
      terminated as provided hereunder, shall continue in full force and effect
      until the expiration of the last to expire of the Combination Patents,
      after which time HMR will have a fully paid-up, royalty-free and
      irrevocable non-exclusive license under the Sepracor Technology in the
      Territory.

ARTICLE 9 - BREACH AND TERMINATION

9.1   In the event HMR or Sepracor are in material breach of any of the
      respective obligations and conditions contained in this Agreement, the
      other party shall be entitled to give the breaching party written notice
      requiring it to cure such material breach. If such material breach is not
      cured within ninety (90) days after receipt of such written notice, the
      notifying party may seek a determination of damages for the uncured breach
      from the breaching party. If the uncured breach is an uncured material
      breach under Section 20.6 of this Agreement, Sepracor agrees that such
      uncured breach may result in irreparable harm to HMR and HMR may seek
      temporary or permanent injunctive relief or other equitable relief.

9.2   If HMR fails to pay Sepracor Royalties, or any interest thereon, due and
      payable in accordance with the terms of this Agreement, and such Royalties
      or interest are not paid to Sepracor within ninety (90) days after receipt
      of written notice as set forth in Section 9.1 above, Sepracor shall have
      the right to terminate this Agreement by giving written notice thereof to
      HMR, which notice shall take effect immediately upon issuance. In
      addition, immediately upon receipt of such termination notice, HMR shall
      assign to Sepracor the entire right, title, and interest in and to the
      Assigned Patents.

9.3   In the event that one of the parties hereto becomes bankrupt or insolvent,
      a receiver or a trustee is appointed for the property or estate of such
      party and said receiver or trustee is not removed within sixty (60) days,
      or the party makes an assignment for the benefit of its creditors, and
      whether any of the aforesaid events be the outcome of the voluntary act of
      that party, or otherwise, the other party shall be entitled to terminate
      this Agreement forthwith by giving a written notice to the first party.

9.4   Nothing herein shall prevent either party hereto from exercising such
      party's right to obtain temporary or permanent injunctive relief or other
      equitable relief.

                                       13
<PAGE>

ARTICLE 10 - RIGHTS AND OBLIGATIONS UPON TERMINATION

10.1  Termination of this Agreement by either party shall not prejudice the
      rights of such party under this Agreement, at law or in equity or
      otherwise, to seek damages or injunctive relief for any breach of this
      Agreement by the other party hereto.

10.2  The termination of this Agreement for any reason shall be without
      prejudice to (i) Sepracor's right to receive all payments accrued and
      unpaid as of the effective date of such termination, (ii) the provisions
      of Sections 4.5 and 4.6 hereof as to Payment Periods, or any portion
      thereof, prior to the effective date of such termination, and (iii) the
      remedy of either party hereto in respect of any previous breach of any of
      the covenants herein contained.

10.3  Articles 7, 10, 12, 20 and 23 shall survive termination of this Agreement.

ARTICLE 11 - REPRESENTATIONS AND WARRANTIES

11.1  Sepracor represents and warrants to HMR that:

      11.1.1 The execution, delivery and performance of this Agreement by
             Sepracor does not conflict with any agreement, instrument or
             understanding, oral or written, to which it is a party or by which
             it may be bound, and, to the best of its knowledge, does not
             violate any material law or regulation of any court, governmental
             body or administrative or other agency having authority over it;

      11.1.2 Sepracor is not currently a party to, and during the term of this
             Agreement will not enter into, any agreements, oral or written,
             that are inconsistent with its obligations under this Agreement;

      11.1.3 Sepracor is duly organized and validly existing under the laws of
             the state of its incorporation and has full legal power and
             authority to enter into this Agreement;

      11.1.4 Sepracor is not subject to any order, decree or injunction by a
             court of competent jurisdiction which prevents or materially delays
             the consummation of the transactions contemplated by this
             Agreement;

                                       14
<PAGE>

      11.1.5 Sepracor is the sole and exclusive owner or licensee of the
             Assigned Patents, Sepracor Patents and the Sepracor Know-How, all
             of which, to the best of Sepracor's knowledge, are free and clear
             of any liens, charges and encumbrances, and, except for Sepracor's
             Affiliates, no other person, corporate or other private entity, or
             governmental entity or subdivision thereof has, or shall have, any
             claim of control with respect to the Assigned Patents, Sepracor
             Patents and the Sepracor Know-How as they relate to Terfenadine
             Carboxylate Technology or Product; and

      11.1.6 In the Territory, there are no Third Party claims, judgments or
             settlements against or owed by Sepracor pending or, to the
             knowledge of Sepracor, threatened, with respect to the Assigned
             Patents, the Sepracor Patents and the Sepracor Know-How as they
             relate to Terfenadine Carboxylate Technology or Product.

11.2  HMR represents and warrants to Sepracor that:

      11.2.1 The execution, delivery and performance of this Agreement by HMR
             does not conflict with any agreement, instrument or understanding,
             oral or written, to which it is a party or by which it may be
             bound, and, to the best of its knowledge, does not violate any
             material law or regulation of any court, governmental body or
             administrative or other agency having authority over it;

      11.2.2 HMR is not currently a party to, and during the term of this
             Agreement will not enter into, any agreements, oral or written,
             that are inconsistent with its obligations under this Agreement;

      11.2.3 HMR is duly organized and validly existing under the laws of the
             state of its incorporation and has full legal power and authority
             to enter into this Agreement; and

      11.2.4 HMR is not subject to any order, decree or injunction by a court of
             competent jurisdiction which prevents or materially delays the
             consummation of the transactions contemplated by this Agreement.

11.3  THE LIMITED WARRANTIES CONTAINED IN THIS ARTICLE ARE THE SOLE WARRANTIES
      GIVEN BY THE PARTIES AND ARE MADE EXPRESSLY IN LIEU OF AND EXCLUDE ANY
      IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
      TITLE, INFRINGEMENT OR OTHERWISE, AND ALL OTHER EXPRESS OR IMPLIED
      REPRESENTATIONS AND WARRANTIES PROVIDED BY COMMON LAW, STATUTE OR
      OTHERWISE ARE HEREBY DISCLAIMED BY BOTH PARTIES.

                                       15
<PAGE>

ARTICLE 12 - INDEMNIFICATION

12.1  HMR agrees to defend, indemnify and hold harmless, Sepracor, its
      successors and assigns, and its officers, directors, employees, agents,
      Affiliates and any person who controls any of such persons (an
      "Indemnified Sepracor Party") from and against any and all liabilities,
      claims, demands, judgments, losses, costs, damages, fees or expenses
      (including reasonable attorneys', consultants' and other professional fees
      and disbursements of every kind, nature and description incurred by such
      Indemnified Sepracor Party in connection therewith) (collectively,
      "Damages") that such Indemnified Sepracor Party may sustain, suffer or
      incur (a) arising out of or in connection with any product liability
      action brought by a Third Party purchaser or user (or any heir or assign
      thereof) of a Product, including, but not limited to, any actual or
      alleged injury, damage, death or other consequence occurring to any person
      as a result, directly or indirectly, of the possession, use or consumption
      of any Product, whether claimed by reason of breach of warranty,
      negligence, product defect or otherwise, or (b) arising out of or in
      connection with acts or omissions by or on behalf of HMR or any Affiliate
      or Licensee thereof with respect to the manufacture, commercialization,
      marketing, sale or use of any Product.

12.2  Sepracor shall defend, indemnify and hold harmless HMR, its successors and
      assigns, and its officers, directors, employees, agents, Affiliates and
      any person who controls any of such persons (an "Indemnified HMR Party")
      from and against any liabilities, claims, demands, judgments, losses,
      costs, damages or expenses whatsoever (including reasonable attorneys',
      consultants' and other professional fees and disbursements of every kind,
      nature and description incurred by such Indemnified HMR Party in
      connection therewith) (collectively, "Damages") that such Indemnified HMR
      Party may incur to the extent that such Damages are attributed to any
      breach of any representation, warranty, covenant or agreement of Sepracor
      contained in this Agreement.

ARTICLE 13 - CHOICE OF LAW

13.1  The construction, validity and performance of this Agreement shall be
      governed in all respects by the laws of the State of Delaware without
      giving effect to principles of conflict of laws.

ARTICLE 14 - FORCE MAJEURE

14.1  No failure or omission by the parties hereto in the performance of any
      obligation of this Agreement shall be deemed a breach of this Agreement
      nor create any liability if the same shall arise from any cause or causes
      beyond the control of the parties, including, but not limited to, the
      following which, for the purposes of this

                                       16
<PAGE>

      Agreement, shall be regarded as beyond the control of the party in
      question: act of God; acts or omissions of any government or any rules,
      regulations or orders of any governmental authority or any officer,
      department, agency or instrument thereof; fire; storm; flood; earthquake;
      accident; acts of the public enemy; war; rebellion; insurrection; riot;
      invasion; or strikes or lockouts.

ARTICLE 15 - NOTICES

15.1  Any notice required or permitted to be given under this Agreement shall be
      mailed by registered or certified air mail, postage prepaid, addressed to
      the party to be notified at its address stated below, or at such other
      address as may hereafter be furnished in writing to the notifying party,
      or by telefax to the numbers set forth below, or to such changed telefax
      numbers as may thereafter be furnished.

      If to SEPRACOR:   Sepracor Inc.
                        111 Locke Drive
                        Marlborough, MA 01752
                        Attn: Chief Executive Officer
                        Telefax: 508-357-7495

      If to HMR:
                        Hoechst Marion Roussel, Inc.
                        Route 202-206
                        P.O. Box 6800
                        Bridgewater, New Jersey 08807-0800
                        U.S.A.
                        Attention: Vice President, Licensing and Alliances
                        Telefax: 908-231-2257

      With a copy to:
                        Morgan, Lewis & Bockius LLP
                        214 Carnegie Center
                        Princeton, New Jersey 08540
                        Attn: Randall B. Sunberg, Esq.
                        Telefax: 609-520-6639

      Any notice sent under this Article shall be deemed to have been received
      on the date actually received, or (i) five (5) Business Days after being
      mailed in the case of a notice mailed by registered or certified mail,
      postage prepaid; and (ii) one (1) Business Day after being transmitted in
      the case of a notice transmitted via telefax.

                                       17
<PAGE>

ARTICLE 16 - WAIVER

16.1  Any term or provision of this Agreement may be waived at any time by the
      party entitled to the benefit thereof by a written instrument duly
      executed by such party. The failure of any party at any time or times to
      require performance of any provision hereof shall in no manner affect the
      right of such party at a later time to enforce the same or any other
      provision of this Agreement. No waiver of any condition or of the breach
      of any provision of this Agreement in one or more instances shall operate
      or be construed as a waiver of any other condition or subsequent breach.

ARTICLE 17 - ENTIRE AGREEMENT

17.1  This Agreement constitutes the entire agreement between the parties hereto
      concerning the subject matter hereof and any representation, promise or
      condition in connection therewith not incorporated herein shall not be
      binding upon either party. This Agreement, including, without limitation,
      the Schedules attached hereto, are intended to define the full extent of
      the legally enforceable undertakings of the parties hereto, and no promise
      or representation, written or oral, which is not set forth explicitly
      herein is intended by either party to be legally binding.

17.2  This Agreement shall expressly supersede the 1993 License Agreement
      entered by and between Sepracor and HMR (formerly known as Marion Merrell
      Dow Inc.) on June 1, 1993. As of the Closing Date, the 1993 License
      Agreement shall be of no further force or effect.

ARTICLE 18 - ASSIGNMENT

18.1  Except as otherwise provided herein, this Agreement is not assignable
      either in whole or in part without the prior written consent of the other
      party; provided, however, that either party may assign this Agreement to
      any of its Affiliates or to any successor by merger or sale of
      substantially all of the business unit to which the Agreement relates.

18.2  This Agreement will be binding upon successors and permitted assigns of
      the parties and the name of a party appearing herein will be deemed to
      include the name of such party's successors and permitted assigns to the
      extent necessary to carry out the intent of this section.

                                       18
<PAGE>

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

ARTICLE 19 - TITLES

19.1  It is agreed that the marginal headings appearing at the beginning of the
      numbered Articles hereof have been inserted for convenience only and do
      not constitute any part of this Agreement.

ARTICLE 20 - PUBLICITY

20.1  On or shortly after the date hereof, the parties will issue the joint
      press release regarding this Agreement attached hereto as Schedule 20.1
      (the "Joint Press Release").

20.2  After the date hereof, [**] whether to the [**] stating that [**] or had
      [**] insofar as otherwise provided in this Agreement, [**]

      20.2.1 Notwithstanding any other provision in this Agreement, [**] after
             the date hereof, [**] concerning the subject matter of this
             Agreement, [**].

      20.2.2 Notwithstanding anything to the contrary in the foregoing, [**] the
             Agreement, [**] in any [**] including the [**] to this language in
             connection with [**]; provided, however, [**] For the avoidance of
             doubt, the parties agree that, [**] in connection with [**] the
             statements [**]

      20.2.3 Within [**] days of the date hereof, Sepracor shall provide to HMR
             the redacted version of this Agreement that Sepracor proposes to
             submit to the Securities and Exchange Commission (the "SEC"), and
             HMR shall have the right to provide comments thereon. Sepracor
             shall consider HMR's comments in good faith and, to the extent
             permitted by law, will not unreasonably withhold its acceptance of
             such comments. Sepracor shall notify promptly HMR of any comments
             of the SEC with respect to such submission.

20.3  HMR may use the Joint Press Release and any Sepracor announcement
      concerning the subject matter of this Agreement, and any statements made
      in any of the foregoing, without prior notice or approval.

      20.3.1 Notwithstanding anything to the contrary in the foregoing, but
             subject always to Sections 20.4 and 20.5 below, HMR may use
             whatever publicity, news release or public announcements, written
             or oral, whether

                                       19
<PAGE>

             to the public or press, stockholders, investors, customers,
             suppliers or otherwise which it deems, in it sole discretion, to be
             appropriate for the purpose of commercializing the Product in the
             Territory.

      20.3.2 Notwithstanding anything to the contrary in the foregoing, but
             subject always to section 20.5 below, HMR may make reference to the
             ownership and origin of the technology underlying the Agreement,
             including, but not limited to, the outcome of HMR's determination
             of priority of invention between the Assigned Patents and the 542
             application and the basis of such determination, including but not
             limited to the interference arbitrator's decision or opinion.

20.4  Except to the extent set forth in the Joint Press Release, neither party
      shall disclose the material business terms of this Agreement except to the
      extent required by law or regulation.

20.5  The parties acknowledge that the interference proceeding and arbitration
      between them are dissolved and settled by this Agreement, and neither
      party shall refer to the interference arbitrator's decision or opinion as
      a legally binding decision in or determination of the interference or
      arbitration thereof.

20.6  Any publicity, news release or public announcement made out of compliance
      with this Article will be considered a material breach of this Agreement
      subject only to the provisions of Section 9.1.

ARTICLE 21 - UNENFORCEABLE PROVISIONS

21.1  The provisions of this Agreement shall be deemed severable and the
      invalidity or unenforceability of any provision shall not affect the
      validity or enforceability of the other provisions hereof. If any
      provision of this Agreement, or the application thereof to any person or
      entity or any circumstance, is invalid or unenforceable, (i) a suitable
      and equitable provision shall be substituted therefore in order to carry
      out, so far as may be valid and enforceable, the intent and purpose of
      such invalid and unenforceable provision and (ii) the remainder of this
      Agreement and the application of such provision to other persons, entities
      or circumstances shall not be affected by such invalidity or
      unenforceability, nor shall such invalidity or unenforceability affect
      such provision, or the application thereof, in any other jurisdiction.

                                       20
<PAGE>

ARTICLE 22 - CONSTRUCTION

22.1  As used in this Agreement, singular includes the plural and plural
      includes the singular, wherever so required by fact or context.

ARTICLE 23 - HMR OWNERSHIP

23.1  Nothing in this Agreement shall be construed as conveying or transferring
      patent or technology rights of any kind owned by HMR to Sepracor.

23.2  All business decisions, including, but not limited to, decisions
      concerning pricing, reimbursement, package design, sales and promotional
      activities for Product, and the decision to launch or continue to market
      Product in the Territory, shall be within the sole discretion of HMR.

23.3  No right, express or implied, is granted by this Agreement to use in any
      manner any trade name or trademark of HMR. When making reference to any
      HMR trademark relating to Compound, Sepracor shall include an
      acknowledgement that such trademark is the property of HMR. Such
      acknowledgement shall be included in an appropriate manner on, for
      example, any literature, promotional material or advertising. Sepracor
      will not use any of HMR's trademarks or trade names relating to Compound
      in a manner which a Third Party could reasonably consider to compromise
      the quality and goodwill associated therewith.

ARTICLE 24 - EXECUTION

24.1  This Agreement may be executed in counterparts, each of which shall for
      all purposes be deemed an original.

ARTICLE 25 - CLOSING

25.1  The respective obligations of each party to effect the transactions
      contemplated under this Agreement shall be subject to the satisfaction, at
      or prior to the Closing Date of the following conditions (the performance
      of any of which by the other party may be waived in writing by Sepracor or
      HMR).

      25.1.1 Neither Sepracor nor HMR shall be subject to any order, decree or
             injunction by a court of competent jurisdiction which prevents or
             materially delays the consummation of the transactions contemplated
             hereby.

                                       21
<PAGE>

      25.1.2 No statute, rule or regulation shall have been enacted by the
             government, or any governmental agency of the United States or any
             state, municipality or other political subdivision thereof, that
             makes the consummation of the transactions contemplated hereby
             illegal.

      25.1.3 The representations and warranties of the other party shall be
             accurate in all material respects as of the time of the Closing
             Date.

                                       22
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed by their respective duly authorized officers or representatives as of
the day and year first above written.

                                    SEPRACOR INC.

                                    By:  /s/ Timothy J. Barberich
                                        ------------------------------
                                    Name:  Timothy J. Barberich
                                    Title: President & CEO

                                    HOECHST MARION ROUSSEL, INC.

                                    By:  /s/ Peter W. Ladell
                                        ------------------------------
                                    Name:  Peter W. Ladell
                                    Title: Chief Operating Officer

                                       23
<PAGE>

                        SCHEDULE 2.1: FORM OF ASSIGNMENT

                                   ASSIGNMENT

WHEREAS, Sepracor Inc. ("Sepracor"), a Delaware corporation having a place of
business at 111 Locke Drive, Marlborough, Massachusetts 01752, is the sole owner
of U.S. Patent No. 5,375,693, entitled "Methods and Compositions for Treating
Allergic Disorders and Other Disorders using Metabolic Derivatives of
Terfenadine" (the "693 Patent") and U.S. Patent Application Serial No.
08/191,149, entitled "Methods and Compositions for Treating Allergic Disorders
and Other Disorders using Optically Pure Isomers of Metabolic Derivatives of
Terfenadine" (the "149 Application"), and United States patent applications
related thereto; and

WHEREAS, Hoechst Marion Roussel, Inc. ("HMR"), a Delaware corporation having a
place of business at Route 202-206, P.O. Box 6800, Bridgewater, New Jersey
08807, is desirous of obtaining Sepracor's entire right, title, and interest in,
to, and under the 693 Patent, the 149 Application, and United States patent
applications related thereto.

NOW, THEREFORE, in consideration of the premises, one dollar, and other good and
valuable consideration to Sepracor, the receipt and sufficiency of which is
hereby acknowledged, Sepracor hereby assigns to HMR its entire right, title and
interest in, to, and under the 693 Patent and the 149 Application (hereby
incorporated by reference as if fully set forth herein) together with any and
all related United States patent applications, including, but not limited to,
any additions, divisions, continuations, continuations-in-part, reissues,
re-examinations, substitutions, extensions, patent term extensions and renewals
thereof, and patents issuing therefrom, in each case, as fully and entirely as
the same would have been held and enjoyed by Sepracor if this assignment had not
been made.

Sepracor also authorizes and requests that the Commissioner of Patents and
Trademarks of the United States, whose duty it is to issue patents or other
evidence or forms of industrial property protection on applications as
aforesaid, to issue the same to HMR in accordance with the terms of this
instrument.

      IN WITNESS WHEREOF, the undersigned duly authorized representative of
Sepracor has affixed his signature.

SEPRACOR INC.

By: _____________________________         Date: ______________________
       Timothy J. Barberich
       President & CEO

                                        1
<PAGE>

Commonwealth of Massachusetts  )
                               ) SS.:
County of Middlesex            )

      On this _____ day of _________, 1999, before me, a Notary Public in and
for the Commonwealth and County aforesaid, personally appeared Timothy J.
Barberich, to me known and known to me to be the person of that name, who signed
and sealed the foregoing instrument, and he acknowledged the same to be his free
act and deed.

                                                      _________________________,
                                                                  Notary Public.

                                        2
<PAGE>

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

                                 SCHEDULE 1.21:

                                SEPRACOR PATENTS

                                       [**]<PAGE>

                                                                   Exhibit 10.31

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

                                LICENSE AGREEMENT

                                 by and between

                                  SEPRACOR INC.

                                       and

                          HOECHST MARION ROUSSEL, INC.

                                 [EX-US LICENSE]

                                 August 31, 1999

      This document is the confidential information of both parties hereto.
    It should be distributed on a need-to-know basis and kept in secure area.
<PAGE>

                                TABLE OF CONTENTS

                                                                     Page

ARTICLE 1 - DEFINITIONS................................................1

ARTICLE 2 - LICENSE GRANT..............................................5

ARTICLE 3 - PENDING PROCEEDINGS AND ACTIONS............................6

ARTICLE 4 - ROYALTIES..................................................6

ARTICLE 5 - ROYALTY PAYMENTS, REPORTS AND RECORDS......................7

ARTICLE 6 - RIGHTS IN TECHNOLOGY, INVENTIONS AND PATENTS...............9

ARTICLE 7 - INFRINGEMENT INVOLVING PRODUCT............................10

ARTICLE 8 - CONFIDENTIALITY...........................................11

ARTICLE 9 - TERM......................................................12

ARTICLE 10 - BREACH AND TERMINATION...................................12

ARTICLE 11 - RIGHTS AND OBLIGATIONS UPON TERMINATION..................13

ARTICLE 12 - REPRESENTATIONS AND WARRANTIES...........................14

ARTICLE 13 - INDEMNIFICATION..........................................15

ARTICLE 14 - FORCE MAJEURE............................................16

ARTICLE 15 - NOTICES..................................................16

ARTICLE 16 - WAIVER...................................................17

ARTICLE 17 - ENTIRE AGREEMENT.........................................17

ARTICLE 18 - ASSIGNMENT...............................................18

ARTICLE 19 - TITLES...................................................18

ARTICLE 20 - PUBLICITY................................................18

ARTICLE 21 - UNENFORCEABLE PROVISIONS.................................20

ARTICLE 22 - CONSTRUCTION.............................................20

                                        i
<PAGE>

ARTICLE 23 - CHOICE OF LAW............................................20

ARTICLE 24 - HMR OWNERSHIP............................................20

ARTICLE 25 - EXECUTION................................................21

ARTICLE 26 - DISPUTE RESOLUTIONS......................................21

ARTICLE 27 - CLOSING..................................................22

SCHEDULE 1.17     CLAIMS ENCOMPASSING PRODUCT

SCHEDULE 1.19     SEPRACOR PATENTS

SCHEDULE 3.1      RELEASE

SCHEDULE 20.1     JOINT PRESS RELEASE

SCHEDULE 20.2.2   LISTING OF ALLEGRA(R)

SCHEDULE 26       ARBITRATION PROVISIONS

                                       ii
<PAGE>

This License Agreement is made as of this 31st day of August, 1999 (the
"Effective Date") by and between Sepracor Inc. ("Sepracor"), a Delaware
corporation having a place of business at 111 Locke Drive, Marlborough,
Massachusetts 01752, and Hoechst Marion Roussel, Inc. ("HMR"), a Delaware
corporation having a place of business at Route 202-206, P.O. Box 6800,
Bridgewater, New Jersey 08807.

BACKGROUND

WHEREAS, Sepracor owns a portfolio of patents and patent applications generally
directed to Terfenadine Carboxylate Technology and certain know-how relating to
Terfenadine Carboxylate Technology;

WHEREAS, HMR and Sepracor are parties to a number of ongoing actions and
proceedings in various forums and countries, including proceedings in the
Australian, United Kingdom, and European Patent Offices, and actions in Belgium
and England;

WHEREAS, Sepracor is willing to license HMR the exclusive right to use the
Sepracor Technology to develop and sell Product in the Territory; and

WHEREAS, HMR wishes to accept such license.

NOW, THEREFORE, in consideration of the mutual promises, covenants and
agreements hereinafter set forth, the sufficiency of which is hereby
acknowledged, the parties to this Agreement mutually agree as follows:

ARTICLE 1 - DEFINITIONS

For purposes of this Agreement, the following initially capitalized terms in
this Agreement, whether used in the singular or plural, shall have the following
meanings, unless the context clearly requires otherwise:

1.1   Affiliate. "Affiliate" shall mean, with respect to either party hereto,
      any corporation, company, partnership, joint venture or any other entity
      which directly or indirectly controls, is controlled by, or is under
      common control with such party. For purposes of this definition, "control"
      shall mean direct or indirect ownership of at least fifty percent (50%) of
      the outstanding voting securities of the entity.

1.2   Agreement. "Agreement" shall mean this License Agreement, including all
      Schedules hereto.

1.3   Business Day. "Business Day" shall mean a day on which banks are open for
      business in both Marlborough, Massachusetts and Bridgewater, New Jersey.

                                       1
<PAGE>

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

1.4   Combination Patent. "Combination Patent" shall mean any and all foreign
      equivalents of United States Patent Application Serial No. [**] in the
      Territory, and any and all related patent applications in the Territory,
      including any additions, divisions, continuations, continuations-in-part,
      reissues, reexaminations, substitutions, extensions, patent term
      extensions and renewals, and patents issued therefrom.

1.5   Combination Product. "Combination Product" shall mean a Product which is
      comprised in part of Compound, and in part of one or more other active
      ingredients; provided, however, that Combination Product shall not include
      any Product all active ingredients of which are recited in a Live Claim of
      one or more issued Sepracor Patents. Notwithstanding the foregoing,
      Products containing Compound and pseudoephedrine as the only active
      ingredients, including but not limited to the Product currently identified
      by the trademark Allegra-D(R), shall not be considered a Combination
      Product for the purposes of this Agreement.

1.6   Compound. "Compound" shall mean the terfenadine metabolite known as
      terfenadine carboxylate and fexofenadine, also identified by the chemical
      name 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]-
      (alpha)-(alpha)-dimethyl benzeneacetic acid, and any stereoisomer,
      solvate, clathrate, salt, or non-covalent derivative thereof.

1.7   Confidential Information. "Confidential Information" shall mean all
      Sepracor Know-How, and all technical and scientific know-how and
      information, pre-clinical and clinical trial results, computer programs,
      knowledge, technology, means, methods, processes, practices, formulas,
      techniques, procedures, designs, drawings, apparatus, written and oral
      representations of data, specifications, and all other scientific,
      clinical, regulatory, marketing, financial and commercial information or
      data, whether communicated in writing, verbally or electronically, which
      is provided by one party to the other party in connection with this
      Agreement. When Confidential Information is disclosed in a manner other
      than in writing, it shall be reduced to written form, marked
      "Confidential" and transmitted to the receiving party within [**] Business
      Days of disclosure to the receiving party.

1.8   Control or Controlled. "Control" or "Controlled", when used in connection
      with intellectual property rights, shall mean the legal authority or right
      of a party hereto to grant a license or sublicense of intellectual
      property rights to another party hereto, or to otherwise disclose
      proprietary or trade secret information to such other party, without
      breaching the terms of any agreement with a Third Party or
      misappropriating the proprietary or trade secret information of a Third
      Party. Information that is generally known or available to the public as
      of the

                                       2
<PAGE>

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

      Effective Date, or which becomes known or available to the public through
      no fault of the party, shall not be deemed Controlled by a party hereto.

1.9   Dollar. "Dollar" shall mean lawful money of the United States of America.

1.10  Generic Equivalent. "Generic Equivalent" shall mean any pharmaceutical
      product that is sold by a Third Party without the consent or approval of
      HMR or any Affiliate or Licensee thereof, and which includes the same
      Compound as an active ingredient as that used in a particular Product for
      the same indication and by the same route of administration as the
      particular Product. For the purposes of this Section 1.10, an Optically
      Pure stereoisomer of a Compound shall be considered a separate and
      distinct Compound, and solvates, clathrates, salts or noncovalent
      derivatives of a Compound shall be considered one and the same Compound.

1.11  Improvement. "Improvement" shall mean any enhancement of or improvement to
      Terfenadine Carboxylate Technology developed, invented or acquired by, or
      coming under the Control of, Sepracor during the course or term of this
      Agreement.

1.12  Licensee. "Licensee" shall mean any person, corporation, unincorporated
      body, or other entity that is not an Affiliate of HMR and to whom HMR
      grants a sublicense of the rights granted to HMR pursuant to this
      Agreement.

1.13  Live Claim. "Live Claim" shall mean a claim of any issued, unexpired
      patent which has not been withdrawn, canceled or surrendered, or held
      invalid or unenforceable by a court of competent jurisdiction in a final,
      unappealable decision.

1.14  Net Sales. "Net Sales" shall mean the gross amount invoiced by HMR and its
      Affiliates and Licensees on account of sales of Product to Third Parties
      in the Territory, less the total of [**] and/or [**] and other [**] to the
      extent [**] in the [**] and other [**] to the extent [**] in the [**]
      pursuant to [**] or the equivalent thereof.

      Actual Net Sales for any Combination Product (except Product encompassed
      by a Live Claim of an issued Sepracor Patent) shall be multiplied by the
      Combination Allocation Portion (as defined below) attributable to such
      Combination Product. The "Combination Allocation Portion", as used herein,
      shall mean [**] as its [**] only the [**] of the [**] containing as its
      active ingredient [**] and the [**] that are [**] by a [**] to a [**]
      Section 1.14(a)-

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<PAGE>

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

      (f) above. [**] for the other [**] in the [**] that are [**] on the [**]
      for such [**]

1.15  Optically Pure. "Optically Pure" shall mean Compound comprising at least
      ninety percent (90%) by weight of one stereoisomer and ten percent (10%)
      by weight or less of the other stereoisomer.

1.16  Payment Period. "Payment Period" shall mean a calendar quarter ending on
      March 31st, June 30th, September 30th, or December 31st; provided,
      however, that the first Payment Period under this Agreement shall include
      the calender quarter ending September 30, 1999, and the period from March
      1, 1999, to June 30, 1999.

1.17  Product. "Product" shall mean any composition which contains Compound as
      an active ingredient, and that is encompassed by a Live Claim of a
      Sepracor Patent. Product shall include any Product encompassed by a Live
      Claim of an issued Combination Patent. Product containing an Optically
      Pure stereoisomer of a Compound shall be considered a separate and
      distinct Product. Product containing solvates, clathrates, salts or
      noncovalent derivatives of a Compound shall be considered one and the same
      Product. If encompassed by a Live Claim of a Combination Patent, Product
      containing one or more leukotriene inhibitors and fexofenadine shall be
      considered a separate and distinct Product, and not a Combination Product.
      Line extensions of a Product shall be considered one and the same Product;
      for example, the composition currently identified by the trademark
      Allegra-D(R) shall be considered the same Product as the composition
      currently identified by the trademark Allegra(R). For the purposes of this
      Agreement, claims identical or substantially equivalent to those set forth
      in Schedule 1.17 are deemed to be claims that encompass Product as
      specified in Schedule 1.17.

1.18  Sepracor Know-How. "Sepracor Know-How" shall mean all proprietary,
      non-public Terfenadine Carboxylate Technology, including, without
      limitation, processes, techniques, formulas, data, methods, equipment
      designs, know-how, show-how and trade secrets, discoveries, practices,
      inventions, technology, manufacturing procedures, test procedures,
      purification and isolation techniques, instructions, test data and other
      intellectual property, patentable or otherwise, tangible or intangible,
      that are owned or Controlled by Sepracor as of the Effective Date or which
      were developed by or at the request of Sepracor prior to or during the
      term of this Agreement and which are not generally known; provided,
      however, that "Sepracor Know-How" shall not include any HMR information or
      materials.

                                       4
<PAGE>

1.19  Sepracor Patents. "Sepracor Patents" shall mean all patents and patent
      applications in the Territory owned or Controlled by Sepracor at any time
      during the term of this Agreement and relating to Terfenadine Carboxylate
      Technology, including those set forth in Schedule 1.19 hereto as it may be
      updated from time to time, and all additions, divisions, continuations,
      continuations-in-part, reissues, re-examinations, substitutions,
      extensions, supplementary protection certificates, and renewals thereof
      (or foreign equivalents in the Territory of any of the foregoing), and
      patents issued therefrom. The term "Sepracor Patents" includes Combination
      Patents.

1.20  Sepracor Technology. "Sepracor Technology" shall mean the Sepracor
      Patents, Sepracor Know-How and Improvements.

1.21  Terfenadine Carboxylate Technology. "Terfenadine Carboxylate Technology"
      shall mean technology related to Compound, including, but not limited to,
      methods of use, processes, compositions, or formulations thereof.

1.22  Territory. "Territory" shall mean countries of the entire world aside from
      the United States and its territories and possessions as of the Effective
      Date.

1.23  Third Party. "Third Party" shall mean any person, corporation,
      unincorporated body, or other entity other than Sepracor and HMR and their
      respective Affiliates and HMR's Licensees.

ARTICLE 2 - LICENSE GRANT

2.1   Sepracor grants to HMR an exclusive (exclusive even as to Sepracor)
      license to develop, have developed, make, have made, use, market, sell,
      have sold and distribute Product in the Territory under the Sepracor
      Technology, subject to the terms and conditions set forth in this
      Agreement.

2.2   The rights and licenses granted hereunder shall be sublicensable by HMR
      subject to the terms and conditions set forth in this Agreement, provided
      that HMR remains responsible to Sepracor under this Agreement and each
      Licensee confirms in writing to HMR that it agrees to be bound by all of
      the terms and conditions contained in this Agreement.

ARTICLE 3 - PENDING PROCEEDINGS AND ACTIONS

3.1   The parties will execute a mutual release in substantially the same form
      attached as Schedule 3.1, dismissing, withdrawing, releasing or
      terminating any and all proceedings or actions currently pending against
      the other party before any court,

                                       5
<PAGE>

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

      administrative agency, patent authority or other government agency or the
      equivalent thereof in the Territory and pertaining to the subject matter
      of this Agreement. The provisions of Articles 15, 19, 22, 23 and 25 of
      this Agreement shall apply with equal force and effect to the mutual
      release set forth in Schedule 3.1.

3.2   HMR shall not be obligated to deliver to Sepracor any amount payable
      pursuant to Section 4.1.2 prior to Sepracor's or its agent's or
      representative's execution of notifications or other correspondence
      substantially in the forms set forth in Exhibits 1-4, 6 and 7 of Schedule
      3.1.

ARTICLE 4 - ROYALTIES

4.1   In consideration of the rights and licenses granted under the Sepracor
      Technology:

      4.1.1 HMR shall pay to Sepracor a royalty of [**] on the Net Sales of
            Product in the Territory ("Royalties").

      4.1.2 Royalties shall be payable on Net Sales of Product in the Territory,
            on a country by country basis, beginning upon the later of March 1,
            1999, and the date of issuance of a Sepracor Patent in such country
            in the Territory, and continuing on a Product by Product basis until
            the first of the following to occur: (1) with respect to a
            particular Product line, the introduction in such country in the
            Territory of a Generic Equivalent of a Product in such Product line
            by a Third Party without approval or consent of HMR or any Affiliate
            or Licensee thereof; or (2) with respect to all Products, the
            expiration of the last of the Sepracor Patents in such country in
            the Territory. The period during which Royalties shall be payable is
            hereinafter referred to as the "Royalty Period." In those countries
            where Royalties on a Product are payable as of the date of issuance
            of a Sepracor Patent in such country, Royalties payable for the
            month in which the Sepracor Patent issues shall be calculated on a
            pro rata basis, for example, if a Sepracor Patent issues on April
            14th, sixteen thirtieths (16/30) of the total April Net Sales for
            that Product in the country will be used to calculate the Royalties
            due for April of the year of issuance. In addition, on a country by
            country basis, Royalties payable for the month during which
            Royalties on a Product cease to be payable in a country shall also
            be calculated on a pro rata basis.

                                       6
<PAGE>

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

      4.1.3 With respect to that product which is not encompassed by a Live
            Claim of a granted or issued Sepracor Patent, no royalty will be due
            under this Agreement.

ARTICLE 5 - ROYALTY PAYMENTS, REPORTS AND RECORDS

5.1   HMR shall deliver to Sepracor within [**] days following the end of each
      Payment Period, beginning with the first Payment Period, a written report
      (the "Royalty Statement") describing, on a country-by-country basis, for
      the applicable Payment Period:

      (a)   the gross sales during the Payment Period for all Products;

      (b)   the Net Sales during the Payment Period for all Products, and the
            exchange rate used to convert any currency other than Dollars into
            Dollars; and

      (c)   the calculation used to determine the total Royalties due for the
            Payment Period.

5.2   Each Royalty Statement for a Payment Period required by Section 5.1 above
      shall be accompanied by full payment to Sepracor, made in accordance with
      Section 5.3, of Royalties and any interest which may have accrued in
      accordance with Articles 4 and 5.

5.3   With regard to any payments due to Sepracor, the following shall apply:

      (a)   All payments to Sepracor pursuant to this Agreement shall be made by
            wire transfer, to Fleet Bank of Massachusetts, 75 State Street,
            Boston, Massachusetts 02109 (ABA #011000138) to Account No. [**] or
            such other bank or account as Sepracor may from time to time
            designate in writing. All such payments shall be made in Dollars.

      (b)   If Net Sales of any Product for a Payment Period is stated in a
            currency other than Dollars, then, for the purpose of determining
            the amount of Royalties payable to Sepracor such Net Sales shall be
            converted into Dollars using an average exchange rate between those
            two currencies during the Payment Period for which such Royalties
            become due, wherein such calculated average exchange rate is
            calculated as the average of the exchange rates most recently quoted
            in the Wall Street Journal in New York on or before each of the last
            days for (i) each month in the Payment Period, and (ii) the last
            month in the immediately preceding Payment Period. If no such
            exchange rates have been quoted in the Wall Street Journal in New
            York at any time during the twelve (12) month period

                                       7
<PAGE>

            preceding the date on which such Royalties become due, then such Net
            Sales shall be converted to Dollars at the average exchange rate
            used by BankBoston during the Payment Period.

      (c)   Whenever any payment hereunder shall be stated to be due on a day
            which is not a Business Day, such payment shall be made on the
            immediately succeeding Business Day.

      (d)   Payments hereunder shall be considered to be made as of the day on
            which they are received in Sepracor's designated bank account.

      (e)   All payments due to Sepracor hereunder but not paid by HMR on the
            due date thereof shall bear interest at the rate which is the lesser
            of: (i) LIBOR plus two percent (2%) per annum; and (ii) the maximum
            lawful interest rate permitted under applicable law. Such interest
            shall accrue on the balance of unpaid amounts from time to time
            outstanding from the date on which portions of such amounts become
            due and owing until payment thereof in full.

5.4   Any income or other taxes which HMR is required by law to pay or withhold
      on behalf of Sepracor with respect to Royalties, and any interest thereon,
      payable to Sepracor under this Agreement, shall be deducted from the
      amount of such Royalties and any interest due, and paid or withheld, as
      appropriate, by HMR on behalf of Sepracor. Any such tax required to be
      paid or withheld shall be an expense of and borne solely by Sepracor. The
      previous two sentences notwithstanding, the parties hereto will reasonably
      cooperate in completing and filing documents required under the provisions
      of any applicable tax laws or under any other applicable law, in order to
      enable HMR to make such payments to Sepracor without any deduction or
      withholding.

5.5   HMR shall keep and maintain, and shall cause its Affiliates, Licensees and
      assigns to keep and maintain, complete and accurate records and books of
      account in sufficient detail and form so as to enable Royalties and any
      interest payable to be determined, including but not limited to, true and
      accurate records of sales of Products and calculations of Net Sales and
      Royalties. Sepracor shall have the right to audit the records of HMR at
      its own expense (except as otherwise provided in Section 5.6) using HMR's
      independent certified accountants unless good cause can be shown as to why
      such accountants should not be used, in which case Sepracor may elect to
      use any nationally recognized firm of independent certified accountants to
      whom HMR has shown no good cause objection. Such accountants will have
      access on reasonable notice to HMR and its Affiliates' and Licensees'
      records during reasonable business hours for the purpose of verifying the
      Royalties and any interest payable as provided in this Agreement for the
      two preceding years. Notwithstanding the foregoing, this right may not be
      exercised more than once in any calendar year, and once a

                                       8
<PAGE>

      calendar year is audited it may not be reaudited, and said accountant
      shall disclose to Sepracor only information relating solely to the
      accuracy of the Royalty Statements provided to Sepracor and the payments
      made to Sepracor under this Agreement.

5.6   Any adjustment required as a result of an audit conducted under this
      Article shall be made within twenty-five (25) days after the date on
      which the accountant conducting the audit issues a written report to
      Sepracor and HMR containing the results of the audit. If any
      underpayment by HMR is greater than ten percent (10%) of the amount
      previously paid to Sepracor for the relevant Payment Period(s), the
      costs and expenses of the audit shall be paid for by HMR. In the case
      of overpayment, HMR may elect, at its option, to either offset
      Royalties and any interest payable to Sepracor by the amount of the
      overpayment or request reimbursement and HMR shall, within ten (10)
      Business Days of issuance of the auditor's written report, provide
      written notice to Sepracor of its election regarding any overpayment. If
      HMR elects reimbursement of an overpayment, Sepracor shall have the longer
      of a) ten (10) Business Days from its receipt of HMR's written notice,
      or b) twenty-five (25) days after the date on which the accountant
      conducting the audit issues a written report to Sepracor and HMR
      containing the results of the audit, to send HMR the requested
      overpayment reimbursement.

5.7   No part of any amount payable to Sepracor under this Agreement may be
      reduced due to any counterclaim, set-off, adjustment or other right which
      HMR might have against Sepracor, any other party or otherwise, except as
      expressly stated to the contrary in this Agreement.

ARTICLE 6 - RIGHTS IN TECHNOLOGY, INVENTIONS AND PATENTS

6.1   Sepracor agrees to use reasonable efforts to continue, at its sole cost
      and expense, the prosecution of the Sepracor Patents and maintenance of
      the Sepracor Patents and Sepracor Know-How. Prosecution of pending patent
      applications shall mean through final patent office appeal and any
      opposition proceedings or the like, including but not limited to, re-issue
      applications and re-examination proceedings or the equivalent thereof.

6.2   After the Effective Date, Sepracor and HMR shall consult with each other
      in connection with prosecution and maintenance of, and annuities for, the
      Sepracor Patents. Sepracor agrees to provide HMR with a reasonable
      opportunity to comment on all material written correspondence issued by
      the relevant patent office in connection with Sepracor Patents, and
      Sepracor shall notify HMR of the allowance, grant or acceptance of any
      Sepracor Patent. Should Sepracor decide not to pursue or maintain any of
      the Sepracor Patents, it shall first offer to assign such Sepracor Patents
      to HMR before letting such Sepracor Patents lapse.

                                       9
<PAGE>

6.3   Sepracor shall consult and cooperate with HMR in good faith with respect
      to the filing of any patent applications for Improvements and the
      maintenance of patents issued thereon including, without limitation, by
      executing and obtaining from employees and other persons all assignments
      and other documents reasonably required in connection therewith.

ARTICLE 7 - INFRINGEMENT INVOLVING PRODUCT

7.1   In the event that either HMR or Sepracor becomes aware of Third Party
      infringement of any issued Sepracor Patent in the Territory, which
      infringement involves Product, it will notify the other party in writing
      to that effect. Any such notice shall include evidence to support an
      allegation of infringement by such Third Party.

      7.1.1 Except as provided in Section 7.1.3, HMR shall have the right, but
            not the obligation, to enforce (with Sepracor's cooperation and at
            HMR's expense) any Sepracor Patents licensed hereunder against
            infringement by Third Parties. Any recovery or damages derived from
            enforcement of any Sepracor Patent shall be used to first reimburse
            HMR for its documented out-of-pocket legal expenses and costs
            relating to such enforcement, then to reimburse Sepracor for its
            documented out of pocket legal expenses and costs relating to such
            enforcement. Any remaining compensatory damages, such as lost profit
            damages and reasonable royalty damages, shall be treated as Net
            Sales hereunder for which Sepracor shall be entitled to received a
            royalty as provided in Articles 4 and 5 of this Agreement. Any
            punitive damages, exemplary damages, or other enhanced damages shall
            be shared equally by the parties.

      7.1.2 Except as provided in Section 7.1.3, in the event of infringement of
            Sepracor Patents, if HMR does not file suit or enter into
            negotiations with the Third Party infringer of such Sepracor Patents
            within three (3) months of receiving evidence of such infringement
            that provides a reasonable basis for jurisdiction of a court, then
            Sepracor shall have the right, but not the obligation, to enforce
            the Sepracor Patents against such infringement (on its own behalf
            and at its own expense). Any recovery or damages derived from
            enforcement of any Sepracor Patent shall first be used to reimburse
            Sepracor for its documented out of pocket legal expenses and costs
            relating to such enforcement, then to reimburse HMR for its
            documented out of pocket legal expenses and costs relating to such
            enforcement. Any remaining damages shall be divided by allocating
            three quarters of such damages to Sepracor and one quarter of such
            damages to HMR.

                                       10
<PAGE>

      7.1.3 Notwithstanding any other provisions herein, if HMR, or its
            Affiliates or Licensees is not selling any Product encompassed by a
            Live Claim of an issued Combination Patent in the Territory, and
            infringement by a Third Party involves Product encompassed by such a
            Live Claim of an issued Combination Patent, Sepracor shall have the
            right, but not the obligation, to enforce the Combination Patents
            against such infringement (on its own behalf and at its own
            expense), and Sepracor shall retain all recoveries from such
            enforcement.

7.2   In any suit or dispute involving infringement of Sepracor Patents by a
      Third Party, the parties shall cooperate fully. Upon the request and at
      the expense of the party bringing suit, the other party shall make
      available to the party bringing suit at reasonable times and under
      appropriate conditions all relevant assistance. In particular, the parties
      agree to furnish technical and other necessary assistance to each other in
      conducting any litigation involving Product necessary to enforce or defend
      the Sepracor Patents against Third Parties.

ARTICLE 8 - CONFIDENTIALITY

8.1   During the term of this Agreement, and for a period of five (5) years
      thereafter, each party hereto will maintain in confidence all Confidential
      Information disclosed by the other party hereto. Neither party shall use,
      disclose or grant use of such Confidential Information except as required
      under this Agreement. To the extent that disclosure is authorized by this
      Agreement, the disclosing party shall obtain prior agreement from its
      employees, agents, consultants, Affiliates, Licensees or clinical
      investigators to whom disclosure is to be made to hold in confidence and
      not make use of such information for any purpose other than those
      permitted by this Agreement. Each party shall use at least the same
      standard of care as it uses to protect its own Confidential Information to
      ensure that such employees, agents, consultants Affiliates, Licensees and
      clinical investigators do not disclose or make any unauthorized use of
      such Confidential Information. Each party shall promptly notify the other
      upon discovery of any unauthorized use or disclosure of Confidential
      Information. Confidential Information shall not include any information
      which:

      8.1.1 was already known to the receiving party, other than under an
            obligation of confidentiality, at the time of disclosure by the
            other party;

      8.1.2 was generally available to the public or otherwise part of the
            public domain at the time of its disclosure to the other party;

      8.1.3 becomes generally available to the public or otherwise part of the
            public domain after its disclosure and other than through any act or
            omission of the receiving party in breach of this Agreement;

                                       11
<PAGE>

      8.1.4 was disclosed to the receiving party, other than under an obligation
            of confidentiality, by a Third Party who had no obligation to the
            other party not to disclose such information; or

      8.1.5 was independently developed by the receiving party without reference
            to the disclosure by the other party.

8.2   The parties agree that the material financial terms of the Agreement shall
      be considered the Confidential Information of both parties.

8.3   Each party may disclose the Confidential Information to the extent such
      disclosure is reasonably necessary in filing or prosecuting patent
      applications, prosecuting or defending litigation, or complying with any
      applicable statute or governmental regulation. In addition, either party
      may disclose Confidential Information to its Affiliates, and HMR may
      disclose such Confidential Information to its Licensees; provided,
      however, in connection with any such disclosure the disclosing party shall
      use diligent efforts to secure confidential treatment of such information.

8.4   The parties shall undertake to ensure that all their employees who have
      access to Confidential Information of the other party are under
      obligations of confidentiality fully consistent with those provided in
      this Article 8.

ARTICLE 9 - TERM

9.1   This Agreement will commence as of the Effective Date and, unless sooner
      terminated as provided hereunder, shall continue in full force and effect
      on a country-by-country basis in the Territory until the expiration of the
      last to expire of Sepracor Patents in a country, at which point HMR will
      have a fully paid-up, royalty-free and irrevocable non-exclusive license
      under the Sepracor Technology in such country.

ARTICLE 10 - BREACH AND TERMINATION

10.1  In the event HMR or Sepracor are in material breach of any of the
      respective obligations and conditions contained in this Agreement, the
      other party shall be entitled to give the breaching party written notice
      requiring it to cure such material breach. If such material breach is not
      cured within ninety (90) days after receipt of such written notice, the
      notifying party may seek a determination of damages for the uncured breach
      from the breaching party. If the uncured breach is an uncured material
      breach under Section 20.6 of this Agreement, Sepracor agrees that such
      uncured breach may result in irreparable harm to HMR and HMR may seek
      temporary or permanent injunctive relief or other equitable relief.

                                       12
<PAGE>

10.2  HMR may terminate this Agreement for any reason by giving Sepracor sixty
      (60) days written notice. In the event of such a termination, HMR shall
      relinquish all rights and licenses granted by Sepracor to HMR under the
      Agreement and return all Sepracor Know-How, except for one copy of any
      documents, which shall be retained for solely for the purpose of
      determining any continuing obligations under Articles 8 and 13 of this
      Agreement.

10.3  Sepracor shall have the right to terminate this Agreement, effective
      immediately, if HMR (i) does not comply with the provisions of Article 3
      and Section 27.1.4, or (ii) except as provided in Articles 6 and 7,
      without the consent of the other party, at any time after the Effective
      Date of this Agreement initiates or participates in (a) any proceeding or
      action against Sepracor or its Affiliates involving Compound or Product,
      or (b) any proceeding or action involving Sepracor Technology, in each
      case before any court, administrative or other government agency, or
      patent authority.

10.4  HMR shall have the right to terminate this Agreement, effective
      immediately, if Sepracor (i) does not comply with the provisions of
      Article 3 and Section 27.1.4, or (ii) except as provided in Articles 6 and
      7, without the consent of the other party, at any time after the Effective
      Date of this Agreement initiates or participates in (a) any proceeding or
      action against HMR or its Affiliates involving Compound or Product, or (b)
      any proceeding or action involving HMR's technology relating to Compound,
      in each case before any court, administrative or other government agency,
      or patent authority.

10.5  In the event that one of the parties hereto becomes bankrupt or insolvent,
      a receiver or a trustee is appointed for the property or estate of such
      party and said receiver or trustee is not removed within sixty (60) days,
      or the party makes an assignment for the benefit of its creditors, and
      whether any of the aforesaid events be the outcome of the voluntary act of
      that party, or otherwise, the other party shall be entitled to terminate
      this Agreement forthwith by giving a written notice to the first party.

10.6  Nothing herein shall prevent either party hereto from exercising such
      party's right to obtain temporary or permanent injunctive relief or other
      equitable relief.

ARTICLE 11 - RIGHTS AND OBLIGATIONS UPON TERMINATION

11.1  Termination of this Agreement by either party shall not prejudice the
      rights of such party under this Agreement, at law or in equity or
      otherwise, to seek damages or injunctive relief for any breach of this
      Agreement by the other party hereto.

11.2  The termination of this Agreement for any reason shall be without
      prejudice to (i) Sepracor's right to receive all payments accrued and
      unpaid as of the effective

                                       13
<PAGE>

      date of such termination, (ii) the provisions of Section 5.5 and 5.6
      hereof as to Payment Periods, or any portion thereof, prior to the
      effective date of such termination, and (iii) the remedy of either party
      hereto in respect of any previous breach of any of the covenants herein
      contained.

11.3  Articles 8, 11, 13, 20 and 24 shall survive termination of this Agreement.

ARTICLE 12 - REPRESENTATIONS AND WARRANTIES

12.1  Sepracor represents and warrants to HMR that:

      12.1.1 The execution, delivery and performance of this Agreement by
             Sepracor does not conflict with any agreement, instrument or
             understanding, oral or written, to which it is a party or by which
             it may be bound, and, to the best of its knowledge, does not
             violate any material law or regulation of any court, governmental
             body or administrative or other agency having authority over it;

      12.1.2 Sepracor is not currently a party to, and during the term of this
             Agreement will not enter into, any agreements, oral or written,
             that are inconsistent with its obligations under this Agreement;

      12.1.3 Sepracor is duly organized and validly existing under the laws of
             the state of its incorporation and has full legal power and
             authority to enter into this Agreement;

      12.1.4 Sepracor is not currently subject to any order, decree or
             injunction by a court of competent jurisdiction which prevents or
             materially delays the consummation of the transactions contemplated
             by this Agreement;

      12.1.5 Sepracor is the sole and exclusive owner or licensee of the
             Sepracor Patents and the Sepracor Know-How, all of which, to the
             best of Sepracor's knowledge, are free and clear of any liens,
             charges and encumbrances, and, except for Sepracor's Affiliates, no
             other person, corporate or other private entity, or governmental
             entity or subdivision thereof has, or shall have, any claim of
             control with respect to the Sepracor Patents and the Sepracor
             Know-How as they relate to Terfenadine Carboxylate Technology or
             Product; and

      12.1.6 In the Territory, there are no Third Party claims, judgments or
             settlements against or owed by Sepracor pending or, to the
             knowledge of Sepracor, threatened, with respect to the Sepracor
             Patents and the Sepracor Know-How as they relate to Terfenadine
             Carboxylate Technology or Product.

                                       14
<PAGE>

12.2  HMR represents and warrants to Sepracor that:

      12.2.1 The execution, delivery and performance of this Agreement by HMR
             does not conflict with any agreement, instrument or understanding,
             oral or written, to which it is a party or by which it may be
             bound, and, to the best of its knowledge, does not violate any
             material law or regulation of any court, governmental body or
             administrative or other agency having authority over it;

      12.2.2 HMR is not currently a party to, and during the term of this
             Agreement will not enter into, any agreements, oral or written,
             that are inconsistent with its obligations under this Agreement;

      12.2.3 HMR is duly organized and validly existing under the laws of the
             state of its incorporation and has full legal power and authority
             to enter into this Agreement; and

      12.2.4 HMR is not currently subject to any order, decree or injunction by
             a court of competent jurisdiction which prevents or materially
             delays the consummation of the transactions contemplated by this
             Agreement.

12.3  THE LIMITED WARRANTIES CONTAINED IN THIS ARTICLE ARE THE SOLE WARRANTIES
      GIVEN BY THE PARTIES AND ARE MADE EXPRESSLY IN LIEU OF AND EXCLUDE ANY
      IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
      TITLE, INFRINGEMENT OR OTHERWISE, AND ALL OTHER EXPRESS OR IMPLIED
      REPRESENTATIONS AND WARRANTIES PROVIDED BY COMMON LAW, STATUTE OR
      OTHERWISE ARE HEREBY DISCLAIMED BY BOTH PARTIES.

ARTICLE 13 - INDEMNIFICATION

13.1  HMR agrees to defend, indemnify and hold harmless, Sepracor, its
      successors and assigns, and its officers, directors, employees, agents,
      Affiliates and any person who controls any of such persons (an
      "Indemnified Sepracor Party") from and against any and all liabilities,
      claims, demands, judgments, losses, costs, damages, fees or expenses
      (including reasonable attorneys', consultants' and other professional fees
      and disbursements of every kind, nature and description incurred by such
      Indemnified Sepracor Party in connection therewith) (collectively,
      "Damages") that such Indemnified Sepracor Party may sustain, suffer or
      incur (a) arising out of or in connection with any product liability
      action brought by a Third Party purchaser or user (or any heir or assign
      thereof) of a Product, including, but not limited to, any actual or
      alleged injury, damage, death or other consequence occurring to any person
      as a result, directly or indirectly, of

                                       15
<PAGE>

      the possession, use or consumption of any Product, whether claimed by
      reason of breach of warranty, negligence, product defect or otherwise, or
      (b) arising out of or in connection with acts or omissions by or on behalf
      of HMR or any Affiliate or Licensee thereof with respect to
      themanufacture, commercialization, marketing, sale or use of any Product.

13.2  Sepracor shall defend, indemnify and hold harmless HMR, its successors and
      assigns, and its officers, directors, employees, agents, Affiliates and
      any person who controls any of such persons (an "Indemnified HMR Party")
      from and against any liabilities, claims, demands, judgments, losses,
      costs, damages or expenses whatsoever (including reasonable attorneys',
      consultants' and other professional fees and disbursements of every kind,
      nature and description incurred by such Indemnified HMR Party in
      connection therewith) (collectively, "Damages") that such Indemnified HMR
      Party may sustain to the extent that such Damages are attributed to any
      breach of any representation, warranty, covenant or agreement of Sepracor
      contained in this Agreement.

ARTICLE 14 - FORCE MAJEURE

14.1  No failure or omission by the parties hereto in the performance of any
      obligation of this Agreement shall be deemed a breach of this Agreement
      nor create any liability if the same shall arise from any cause or causes
      beyond the control of the parties, including, but not limited to, the
      following which, for the purposes of this Agreement, shall be regarded as
      beyond the control of the party in question: act of God; acts or omissions
      of any government or any rules, regulations or orders of any governmental
      authority or any officer, department, agency or instrument thereof; fire;
      storm; flood; earthquake; accident; acts of the public enemy; war;
      rebellion; insurrection; riot; invasion; or strikes or lockouts.

ARTICLE 15 - NOTICES

15.1  Any notice required or permitted to be given under this Agreement shall be
      mailed by registered or certified air mail, postage prepaid, addressed to
      the party to be notified at its address stated below, or at such other
      address as may hereafter be furnished in writing to the notifying party or
      by telefax to the numbers set forth below or to such changed telefax
      numbers as may thereafter be furnished.

      If to SEPRACOR:   Sepracor Inc.
                        111 Locke Drive
                        Marlborough, MA 01752
                        Attn: Chief Executive Officer
                        Telefax: 508-357-7495

      If to HMR:

                                       16
<PAGE>

                        Hoechst Marion Roussel, Inc.
                        Route 202-206
                        P.O. Box 6800
                        Bridgewater, New Jersey 08807-0800
                        U.S.A.
                        Attention: Vice President, Licensing and Alliances
                        Telefax: 908-231-2257

With a copy to:
                        Morgan, Lewis & Bockius LLP
                        214 Carnegie Center
                        Princeton, New Jersey 08540
                        Attn: Randall B. Sunberg, Esq.
                        Telefax: 609-520-6639

Any notice sent under this Article shall be deemed to have been received on the
date actually received, or (i) five (5) Business Days after being mailed in the
case of a notice mailed by registered or certified mail, postage prepaid; and
(ii) one (1) Business Day after being transmitted in the case of a notice
transmitted via telefax.

ARTICLE 16 - WAIVER

16.1  Any term or provision of this Agreement may be waived at any time by the
      party entitled to the benefit thereof by a written instrument duly
      executed by such party. The failure of any party at any time or times to
      require performance of any provision hereof shall in no manner affect the
      right of such party at a later time to enforce the same or any other
      provision of this Agreement. No waiver of any condition or of the breach
      of any provision of this Agreement in one or more instances shall operate
      or be construed as a waiver of any other condition or subsequent breach.

ARTICLE 17 - ENTIRE AGREEMENT

17.1  This Agreement constitutes the entire agreement between the parties hereto
      concerning the subject matter hereof and any representation, promise or
      condition in connection therewith not incorporated herein shall not be
      binding upon either party. This Agreement, including, without limitation,
      the Schedules attached hereto, are intended to define the full extent of
      the legally enforceable undertakings of the parties hereto, and no promise
      or representation, written or oral, which is not set forth explicitly
      herein is intended by either party to be legally binding.

                                       17
<PAGE>

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

ARTICLE 18 - ASSIGNMENT

18.1  Except as otherwise provided herein, this Agreement is not assignable
      either in whole or in part without the prior written consent of the other
      party; provided, however, that either party may assign this Agreement to
      any of its Affiliates or to any successor by merger or sale of
      substantially all of the business unit to which the Agreement relates.

18.2  This Agreement will be binding upon successors and permitted assigns of
      the parties and the name of a party appearing herein will be deemed to
      include the name of such party's successors and permitted assigns to the
      extent necessary to carry out the intent of this section.

ARTICLE 19 - TITLES

19.1  It is agreed that the marginal headings appearing at the beginning of the
      numbered Articles hereof have been inserted for convenience only and do
      not constitute any part of this Agreement.

ARTICLE 20 - PUBLICITY

20.1  On or shortly after the date hereof, the parties will issue the joint
      press release regarding this Agreement attached hereto as Schedule 20.1
      (the "Joint Press Release").

20.2  After the date hereof, [**] whether to the [**] stating that [**] or had
      [**] insofar as otherwise provided in this Agreement, [**]

      20.2.1 Notwithstanding any other provision in this Agreement, [**] after
             the date hereof, [**] concerning the subject matter of this
             Agreement, [**].

      20.2.2 Notwithstanding anything to the contrary in the foregoing, [**] the
             Agreement, [**] in any [**] including the [**] to this language in
             connection with [**]; provided, however, [**] For the avoidance of
             doubt, the parties agree that, [**] in connection with [**] the
             statements [**]

      20.2.3 Within [**] days of the date hereof, Sepracor shall provide to HMR
             the redacted version of this Agreement that Sepracor proposes to
             submit to the Securities and Exchange Commission (the "SEC"), and
             HMR shall have the right to provide comments thereon. Sepracor
             shall consider

                                       18
<PAGE>

             HMR's comments in good faith and, to the extent permitted by law,
             will not unreasonably withhold its acceptance of such comments.
             Sepracor shall notify promptly HMR of any comments of the SEC with
             respect to such submission.

20.3  HMR may use the Joint Press Release and any Sepracor announcement
      concerning the subject matter of this Agreement, and any statements made
      in any of the foregoing, without prior notice or approval.

      20.3.1 Notwithstanding anything to the contrary in the foregoing, but
             subject always to Sections 20.4 and 20.5 below, HMR may use
             whatever publicity, news release or public announcements, written
             or oral, whether to the public or press, stockholders, investors,
             customers, suppliers or otherwise which it deems, in it sole
             discretion, to be appropriate for the purpose of commercializing
             the Product in the Territory.

      20.3.2 Notwithstanding anything to the contrary in the foregoing, , but
             subject always to section 20.5 below, HMR may make reference to the
             ownership and origin of the technology underlying the Agreement,
             including, but not limited to, the outcome of HMR's determination
             of priority of invention between the Assigned Patents and the 542
             application and the basis of such determination, including but not
             limited to the interference arbitrator's decision or opinion.

20.4  Except to the extent set forth in the Joint Press Release, neither party
      shall disclose the material business terms of this Agreement except to the
      extent required by law or regulation.

20.5  The parties acknowledge that the interference proceeding and arbitration
      between them are dissolved and settled by this Agreement, and neither
      party shall refer to the interference arbitrator's decision or opinion as
      a legally binding decision in or determination of the interference or
      arbitration thereof.

20.6  Any publicity, news release or public announcement made out of compliance
      with this Article will be considered a material breach of this Agreement
      subject only to the provisions of Section 10.1.

ARTICLE 21 - UNENFORCEABLE PROVISIONS

21.1  The provisions of this Agreement shall be deemed severable and the
      invalidity or unenforceability of any provision shall not affect the
      validity or enforceability of the other provisions hereof. If any
      provision of this Agreement, or the application thereof to any person or
      entity or any circumstance, is invalid or

                                       19
<PAGE>

      unenforceable, (i) a suitable and equitable provision shall be substituted
      therefore in order to carry out, so far as may be valid and enforceable,
      the intent and purpose of such invalid and unenforceable provision and
      (ii) the remainder of this Agreement and the application of such provision
      to other persons, entities or circumstances shall not be affected by such
      invalidity or unenforceability, nor shall such invalidity or
      unenforceability affect such provision, or the application thereof, in any
      other jurisdiction.

ARTICLE 22 - CONSTRUCTION

22.1  As used in this Agreement, singular includes the plural and plural
      includes the singular, wherever so required by fact or context.

ARTICLE 23 - CHOICE OF LAW

23.1  The construction, validity and performance of this Agreement shall be
      governed in all respects by the laws of the United Kingdom, without giving
      effect to principles of conflict of laws and any suit brought pursuant to
      this Agreement shall be filed in the appropriate forum in London, England.

ARTICLE 24 - HMR OWNERSHIP

24.1  Nothing in this Agreement shall be construed as conveying or transferring
      patent or technology rights of any kind owned by HMR to Sepracor.

24.2  All business decisions, including, but not limited to, decisions
      concerning pricing, reimbursement, package design, sales and promotional
      activities for Product, and the decision to launch or continue to market
      Product in the Territory, shall be within the sole discretion of HMR.

24.3  No right, express or implied, is granted by this Agreement to use in any
      manner any trade name or trademark of HMR. When making reference to any
      HMR trademark relating to Compound, Sepracor shall include an
      acknowledgement that such trademark is the property of HMR. Such
      acknowledgement shall be included in an appropriate manner on, for
      example, any literature, promotional material or advertising. Sepracor
      will not use any of HMR's trademarks or trade names relating to Compound
      in a manner which a Third Party could reasonably consider to compromise
      the quality and goodwill associated therewith.

ARTICLE 25 - EXECUTION

25.1  This Agreement may be executed in counterparts, each of which shall for
      all purposes be deemed an original.

                                       20
<PAGE>

ARTICLE 26 - DISPUTE RESOLUTIONS

26.1  In the event any dispute, difference or question arises between the
      parties pertaining to or in connection with whether a Product is
      encompassed by a Live Claim of a Sepracor Patent in a country in the
      Territory, then such dispute shall be resolved in the step-wise process
      set forth in Sections 26.1(a) to (d) below.

      (a)   Promptly upon receiving notice of the expected issuance or grant of
            a Sepracor Patent in a particular country, HMR shall make a good
            faith, reasonable determination as to whether the Product is
            encompassed by a Live Claim of a Sepracor Patent in that country.

      (b)   If in good faith HMR reasonably determines that such Product is not
            encompassed by a Live Claim of a Sepracor Patent in the country, HMR
            shall provide Sepracor with written notification of its
            determination, and the parties shall meet and discuss the reasons
            for HMR's determination.

      (c)   If the parties' discussions do not resolve the dispute as to whether
            a Product is encompassed by a Live Claim of a Sepracor Patent in the
            country, the parties shall jointly retain a mutually acceptable
            attorney with expertise in the field of patents and/or intellectual
            property rights in the relevant country to render an independent
            expert opinion on the issue. If both parties agree in writing with
            the independent expert's opinion, it will be binding upon the
            parties.

      (d)   If either party does not agree in writing with the independent
            expert's opinion, within thirty (30) days of the receipt of the
            opinion, the disagreeing party may submit the disputed matter to
            binding arbitration in accordance with Schedule 26. If the disputed
            matter is not submitted to binding arbitration within the thirty
            (30) day period, the expert opinion will be final and binding on the
            parties for the purpose of determining whether the Product at issue
            is encompassed by a Live Claim of a Sepracor Patent in the country
            at issue.

ARTICLE 27 - CLOSING

27.1  The respective obligations of each party to effect the transactions
      contemplated under this Agreement shall be subject to the satisfaction, at
      or prior to the Effective Date of the following conditions (the
      performance of any of which by the other party may be waived in writing by
      Sepracor or HMR).

      27.1.1 Neither Sepracor nor HMR shall be subject to any order, decree or
             injunction by a court of competent jurisdiction which prevents or

                                       21
<PAGE>

             materially delays the consummation of the transactions contemplated
             hereby.

      27.1.2 No statute, rule or regulation shall have been enacted by the
             government, or any governmental agency of the United States or any
             state, municipality or other political subdivision thereof, that
             makes the consummation of the transactions contemplated hereby
             illegal.

      27.1.3 The representations and warranties of the other party shall be
             accurate in all material respects as of the time of the Effective
             Date and such other party shall have delivered a certificate of an
             officer certifying the same.

      27.1.4 The parties shall have executed a mutual release in substantially
             the form attached as Schedule 3.1, dismissing, withdrawing,
             releasing or terminating without prejudice any and all actions or
             proceedings currently pending against the other party before any
             court, administrative agency, patent authority or other government
             agency or the equivalent thereof in the Territory and pertaining to
             the subject matter of this Agreement.

                                       22
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed by their respective duly authorized officers or representatives as of
the day and year first above written.

                                    SEPRACOR INC.

                                    By:  /s/ Timothy J. Barberich
                                        ------------------------------
                                    Name:  Timothy J. Barberich
                                    Title: President & CEO

                                    HOECHST MARION ROUSSEL, INC.

                                    By:  /s/ Peter W. Ladell
                                        ------------------------------
                                    Name:  Peter W. Ladell
                                    Title: Chief Operating Officer
<PAGE>

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

                                 SCHEDULE 1.19:

                                SEPRACOR PATENTS

                                       [**]

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