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

                                                                  Exhibit 10.21


                            MASTER SERVICES AGREEMENT

         This Master Services Agreement ("Agreement") is made on this 25 day of
February, 2003, between Idenix Pharmaceuticals, Inc., a Delaware corporation
having its principal place of business at 125 Cambridge Park Drive, 3rd Floor,
Cambridge, Massachusetts 02140, on behalf of itself and its affiliates
(hereinafter "Sponsor"), and Quintiles, Inc., a North Carolina corporation
having its principal place of business at 5927 South Miami Boulevard,
Morrisville, North Carolina 27560-8396 (hereinafter "Quintiles"). When signed by
both parties, this Agreement will set forth the terms and conditions under which
Quintiles agrees to provide certain services to Sponsor as set forth herein.

                                    RECITALS:

         A.       Sponsor is in the business of discovering, developing,
manufacturing and/or commercializing pharmaceutical products. Quintiles is in
the business of providing clinical trial services, research, and other services
for the pharmaceutical, medical device and biotechnology industries.

         B.       Sponsor and Quintiles desire to enter into this Agreement to
provide the terms and conditions upon which Sponsor may engage Quintiles from
time-to-time to provide services for individual studies or projects by executing
individual Work Orders (as defined below) specifying the details of the services
and the related terms and conditions.

                                   AGREEMENT:

1.0      SCOPE OF THE AGREEMENT; WORK ORDERS; NATURE OF SERVICES.

         (a)      Scope of Agreement. As a "master" form of contract, this
                  Agreement allows the parties to contract for multiple projects
                  through the issuance of multiple Work Orders (as discussed in
                  Section 1.0 (b) below), without having to re-negotiate the
                  basic terms and conditions contained herein. This Agreement
                  covers the provision of services by Quintiles and Quintiles'
                  corporate affiliates (as provided in Section 17) and,
                  accordingly, this Agreement represents a vehicle by which
                  Sponsor can efficiently contract with Quintiles and its
                  corporate affiliates for a broad range of services.

         (b)      Work Orders. The specific details of each project under this
                  Agreement (each "Project") shall be separately negotiated and
                  specified in writing on terms and in a form acceptable to the
                  parties (each such writing, a "Work Order"). A sample Work
                  Order is attached hereto as Exhibit A. Each Work Order will
                  include, as appropriate, the scope of work, time line, budget
                  and payment schedule, and other relevant terms. Each Work
                  Order shall be subject to all of the terms and conditions of
                  this Agreement, in addition to the specific details set forth
                  in the Work Order. To the extent any terms or provisions of a
                  Work Order conflict with the terms and provisions of this
                  Agreement, the terms and provisions of this Agreement shall
                  control, except to the extent that the applicable Work Order
                  expressly and specifically states an intent to supersede the
                  Agreement on a


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                  specific matter. All Work Orders and other exhibits hereto
                  shall be deemed to be incorporated herein by reference.

         (c)      Nature of Services. The services covered by this Agreement may
                  include strategic planning, expert consultation, clinical
                  trial services, statistical programming and analysis, data
                  processing, data management, regulatory, clerical, project
                  management, central laboratory services, preclinical services,
                  pharmaceutical sciences services, medical device services, and
                  other research and development services requested by Sponsor
                  and agreed to by Quintiles as set forth in the relevant Work
                  Order (collectively, the "Services"). Quintiles and Sponsor,
                  where appropriate, shall cooperate in the completion of a
                  Transfer of Obligations Form in conjunction with the relevant
                  Work Order. Any responsibilities not specifically transferred
                  in the Transfer of Obligations Form shall remain the
                  regulatory responsibility of Sponsor. The Transfer of
                  Obligations Form will be filed with the Food and Drug
                  Administration ("FDA") by Sponsor where appropriate, or as
                  required by law or regulation.

         (d)      Existing Agreement. The parties expressly acknowledge that the
                  Sponsor has executed a Master Services Agreement with
                  Quintiles Scotland Ltd, dated as of May 27, 1999, and that
                  such Master Services Agreement remains in full force and
                  effect and shall not be terminated, superceded, amended or
                  otherwise affected by this Agreement.

2.0      PAYMENT OF FEES AND EXPENSES. Sponsor will pay Quintiles for fees,
         expenses and pass-through costs in accordance with the budget and
         payment schedule contained in each Work Order. The aggregate fees and
         expenses payable by Sponsor to Quintiles for any Work Order shall not
         exceed the total fees and expenses included in the applicable budget
         and payment schedule for such Work Order, unless otherwise authorized
         in advance by Sponsor. Pass-through expenses for any Work Order [**]
         pass-through expenses in the applicable budget and payment schedule
         [**} by Sponsor. Sponsor agrees that the budget and payment schedule
         for each Work Order will be structured in an effort to maintain cash
         neutrality for Quintiles (with respect to the payment of professional
         fees, pass-through costs and otherwise). Sponsor agrees that, upon
         request by Quintiles, it will make an up-front payment (the "Prepayment
         Amount".) The Prepayment Amount will be mutually agreed upon by the
         parties on a Project-by-Project basis. Unless otherwise agreed in a
         particular Work Order, the Prepayment Amount will be credited against
         amounts otherwise owed by Sponsor on the final invoice relating to such
         Work Order. Unless otherwise agreed in a particular Work Order, the
         following shall apply: (a) Quintiles will invoice Sponsor monthly for
         the fees, expenses and pass-through costs incurred in performing the
         Services, and shall provide a standard expense statement substantiating
         all such expenses and pass-through costs with each invoice; and, (b)
         Sponsor shall pay each invoice within thirty (30) days of the date of
         Sponsor's receipt of the invoice. If any portion of an invoice is
         disputed, then Sponsor shall pay the undisputed amounts as set forth in
         the preceding sentence and the parties shall use good faith efforts to
         reconcile the disputed amount as soon as practicable. Quintiles may
         assess interest in an amount equal to one percent (1%) per month (or
         the maximum lesser amount permitted by law) of all


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         undisputed amounts owing hereunder and not paid within [**] days of the
         Sponsor's receipt of the invoice.

3.0      TERM. This Agreement shall commence on the date it has been signed by
         all parties and indicated in the first paragraph of this Agreement and
         shall continue for a period of five (5) years, or until terminated by
         either party in accordance with Section 16 below. The Agreement will
         automatically renew each year thereafter for a period of one year,
         unless terminated in accordance with Section 16 below.

4.0      CHANGE ORDERS. Any material change in the scope of a Work Order or the
         stated assumptions upon which the Work Order is based (including, but
         not limited to, changes in an agreed starting date for a Project or
         suspension of the Project by Sponsor) may require changes in the budget
         and/or time lines. After discussion with and approval of Sponsor,
         Quintiles shall generate a written amendment to the Work Order (a
         "Change Order"). A sample Change Order form is attached hereto as
         Exhibit C. Each Change Order shall detail the requested changes to the
         applicable task, responsibility, duty, budget, time line or other
         matter. The Change Order will become effective upon the execution of
         the Change Order by both parties, and Quintiles will be given a
         reasonable period of time within which to implement the changes. Both
         parties agree to act in good faith and promptly when considering a
         Change Order requested by the other party. Quintiles reserves the right
         to postpone effecting material changes in the Project's scope until
         such time as the parties agree to the final terms of and execute the
         corresponding Change Order. For any Change Order that affects the scope
         of the regulatory obligations that have been transferred to Quintiles,
         Quintiles and Sponsor shall execute a corresponding amendment to the
         Transfer of Obligations Form. Sponsor shall file such amendment where
         appropriate, or as required by law or regulation.

5.0      CONFIDENTIALITY. It is understood that during the course of this
         Agreement, Quintiles and employees, officers, directors, agents and
         representatives (collectively "Representatives") of Quintiles may be
         exposed to material, data and information that are confidential and
         proprietary to Sponsor. All such data and information, including but
         not limited to any protocol, investigator brochure, clinical trial
         data, chemical compounds, study drugs, materials, trade secrets,
         intellectual property and other assets, know-how, processes, technical,
         scientific, financial or business information of any kind, whether in
         written, oral, electronic, magnetic, optical, tangible or intangible
         form (hereinafter "Sponsor Confidential Information"), made available,
         disclosed, or otherwise made known to or generated by Quintiles and its
         Representatives as a result of Services under this Agreement shall be
         considered confidential and shall be considered the sole property of
         Sponsor. All information regarding Quintiles' operations, methods, and
         pricing and all Quintiles' Property (as defined in Section 6.0 below),
         disclosed by Quintiles to Sponsor in connection with this Agreement is
         proprietary, confidential information belonging to Quintiles (the
         "Quintiles Confidential Information", and together with the Sponsor
         Confidential Information, the "Confidential Information"). The
         Confidential Information shall be used by the receiving party and its
         Representatives only for purposes of performing the receiving party's
         obligations hereunder. Each party agrees that it will not reveal,
         publish or otherwise disclose the Confidential Information of the other
         party to any third party without the prior written consent of the
         disclosing party. Except as may


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<PAGE>

         be-required by-law, each party agrees that it will not disclose the
         terms of this Agreement including but not limited to the budget and
         payment schedule of any Work Order to any third party without the
         written consent of the other party, which shall not unreasonably be
         withheld; provided however, that Sponsor may disclose the portion of
         this Agreement to its affiliates, agents, representatives (not
         competitors of Quintiles) or its licensing partners who have a need to
         know and who are bound by the obligations of confidentiality and use
         similar to those set forth in this Section 5.0. These obligations of
         confidentiality and nondisclosure shall remain in effect for a period
         of ten (10) years after the completion or termination of the applicable
         Work Order.

         The foregoing obligations shall not apply to Confidential Information
         to the extent that it: (a) is or becomes generally available to the
         public other than as a result of a disclosure by the receiving party;
         (b) becomes available to the receiving party on a non-confidential
         basis from a source which is not prohibited from disclosing such
         information; (c) was developed independently of any disclosure by the
         disclosing party or was known to the receiving party prior to its
         receipt from the disclosing party, as shown by contemporaneous written
         evidence; or, (d) is required by law or regulation to be disclosed,
         provided however that, to the extent practicable, the receiving party
         shall provide prior notice of such disclosure to the disclosing party
         and take all practicable reasonable and lawful actions to cooperate
         with the disclosing party in connection with the disclosing party's
         efforts to avoid and /or minimize the extent of such disclosure.

6.0      OWNERSHIP AND INVENTIONS. All data and information generated or derived
         by Quintiles as the result of services performed by Quintiles under
         this Agreement shall be and remain the exclusive property of Sponsor.
         Any discoveries, developments, improvements or inventions, whether or
         not patentable that may evolve from the Sponsor Confidential
         Information, the data and information described above, and/or be
         conceived and/or reduced to practice and/or evolve within the scope of
         and as the result of services performed by Quintiles under this
         Agreement (collectively "Inventions"), shall belong to Sponsor.
         Quintiles agrees to promptly disclose all such Inventions to Sponsor,
         to assign all of its rights, title and interest, and to cause its
         Representatives to execute such assignments, in all such Inventions
         and/or related patents to Sponsor. Quintiles further agrees to use
         reasonable efforts to assist Sponsor, at Sponsor's cost and expense, to
         file patent applications or to obtain other intellectual property
         protection on such Inventions. Notwithstanding the foregoing, Sponsor
         acknowledges that Quintiles possesses certain inventions, processes,
         know-how, trade secrets, improvements, other intellectual properties
         and other assets, including but not limited to analytical methods,
         procedures and techniques, procedure manuals, personnel data, financial
         information, computer technical expertise and software, which have been
         independently developed by Quintiles and which relate to its business
         or operations (collectively "Quintiles' Property"). Sponsor and
         Quintiles agree that any Quintiles' Property or improvements thereto
         which are used, improved, modified or developed by Quintiles under or
         during the term of this Agreement are the sole and exclusive property
         of Quintiles.

7.0      RECORDS AND MATERIALS. At the completion of the Services by Quintiles,
         or upon termination of this Agreement and/or any Work Order(s), all
         Sponsor Confidential Information, study drugs, materials, information
         and all other data owned by Sponsor,


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<PAGE>

         regardless of the method of storage or retrieval, shall be delivered to
         Sponsor in such form as is then currently in the possession of
         Quintiles, subject to the payment obligations set forth in Section 2
         herein. Alternatively, at Sponsor's written request, such materials and
         data may be retained by Quintiles for Sponsor for an agreed-upon time
         period, or disposed of pursuant to the written directions of Sponsor.
         Sponsor shall pay the costs associated with any of the above options
         and shall pay a to-be-determined fee for storage by Quintiles of
         records and materials after completion or termination of the Services.
         Quintiles, however, reserves the right to retain, at its own cost and
         subject to the confidentiality provisions herein, copies of all
         materials that may be needed to satisfy regulatory requirements or to
         resolve disputes regarding the Services. Nothing in this Agreement
         shall be construed to transfer from Sponsor to Quintiles any FDA or
         regulatory record-keeping requirements unless such transfer is
         specifically provided for in the applicable Transfer of Obligations
         Form.

8.0      INDEPENDENT CONTRACTOR RELATIONSHIP. For the purposes of this
         Agreement, the parties hereto are independent contractors and nothing
         contained in this Agreement shall be construed to place them in the
         relationship of partners, principal and agent, employer/employee or
         joint venturers. Neither party shall have the power or right to bind or
         obligate the other party, and neither party shall hold itself out as
         having such authority [**] the parties will include [**] to the extent,
         and under the terms, set forth [**].

9.0      REGULATORY COMPLIANCE; INSPECTIONS. Quintiles certifies and represents
         that its Services will be conducted in compliance with this Agreement,
         each applicable Work Order, the Protocol, Sponsor's written
         instructions provided to and agreed to by Quintiles, and all applicable
         laws, rules and regulations, including but not limited to the Federal
         Food, Drug and Cosmetic Act and the regulations promulgated pursuant
         thereto, the applicable laws, rules and regulations of each country in
         which Services will be conducted, International Conference on
         Harmonization of Technical Requirements for Registration of
         Pharmaceuticals for Human Use Guidelines ("ICH Guidelines"), Good
         Clinical Practice ("GCP"), and with the standard of care customary in
         the contract research organization industry. Regarding the FDA's
         electronic records and signatures regulation, 21 CFR Part 11 ("Part
         11"), Quintiles has a compliance plan in place as to its applicable
         database applications and electronic records systems and it is working
         diligently to implement its plan. Quintiles, however, is not
         responsible for the compliance or noncompliance of applications or
         systems used by third parties (including, but not limited to,
         investigative sites or third party laboratories) unless such
         applications or systems are owned by Quintiles. Quintiles' standard
         operating procedures will be used in performance of the Services,
         unless otherwise specifically stated in the Work Order. Quintiles
         certifies that it has not been debarred under the Generic Drug
         Enforcement Act and that it will not knowingly employ any person or
         entity that has been so debarred, or is currently under investigation,
         to perform any Services under this Agreement. Sponsor


Idenix Quiniles MSA                    5                            CONFIDENTIAL
<PAGE>

         represents and certifies that it will not knowingly require Quintiles
         to perform any assignments or tasks in a manner that would violate any
         applicable law or regulation. Sponsor further represents that it will
         cooperate with Quintiles in taking any actions that Quintiles
         reasonably believes are necessary to comply with the regulatory
         obligations that have been transferred to Quintiles.

         Each party acknowledges that the other party may respond independently
         to any regulatory correspondence or inquiry in which such party or its
         affiliates is named. Each party, however, shall notify the other party
         promptly of any FDA or other governmental or regulatory inspection or
         inquiry concerning any Study or Project of Sponsor in which Quintiles
         is providing Services, including, but not limited to, inspections of
         investigational sites or laboratories. Quintiles shall forward to
         Sponsor copies of any correspondence from any regulatory or
         governmental agency relating to such a Study or Project, including, but
         not limited to, FDA Form 483 notices, and FDA refusal to file,
         rejection or warning letters, even if they do not specifically mention
         the Sponsor. Sponsor shall forward to Quintiles copies of any
         non-routine correspondence from any regulatory or governmental agency
         relating to such a Study or Project that is relevant to, involves or
         affects Quintiles' Services. Each party shall obtain the written
         consent of the other party, which will not be unreasonably withheld,
         before referring to the other party or its affiliates in any regulatory
         correspondence related to an investigation or other non-routine inquiry
         by such regulatory authority, but written consent will not be required
         if the party has not responded within five (5) business days of receipt
         of the requesting party's request for consent. Where reasonably
         practicable, each party will be given the opportunity to have a
         representative present during an FDA or regulatory inspection. Each
         party, however, acknowledges that it may not direct the manner in which
         the other party fulfills its obligations to permit inspection by
         governmental entities.

         Each party agrees that, during an inspection by the FDA or other
         regulatory authority concerning any study or Project of Sponsor in
         which Quintiles is providing Services, it will not disclose the
         Confidential Information, or any other information and materials that
         are not required to be disclosed to such agency, without the prior
         consent of the other party, which shall not unreasonably be withheld.

         During the term of this Agreement, Quintiles will permit Sponsor's
         representatives (unless such representatives are competitors of
         Quintiles) to examine or audit the work performed hereunder and the
         facilities at which the work is conducted upon reasonable advance
         notice during regular business hours to determine that the Services are
         being conducted in accordance with the Work Order and that the
         facilities are adequate. All information disclosed, revealed to or
         ascertained by Sponsor in connection with any such audit or examination
         or in connection with any correspondence between Quintiles and any
         regulatory authorities (including any FDA Form 483 notices) shall be
         deemed to constitute Confidential Information for purposes of this
         Agreement. Quintiles shall bear the costs and expenses incurred by
         Quintiles in connection with: (a) one audit inspection or investigation
         per Project and for any audit; (b) an inspection or investigation that
         results solely from the wrongdoing of Quintiles; or (c) in the event
         that a governmental authority performs a general audit of Quintiles.
         Sponsor shall bear the reasonable costs and expenses of all other
         audits, inspections and investigations related to the Project


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         initiated or requested by Sponsor, or initiated by a governmental
         authority for a Project of Sponsor.

10.0     RELATIONSHIP WITH INVESTIGATORS. If a particular Work Order obligates
         Quintiles to contract with investigators or investigative sites
         (collectively, "Investigators") then Quintiles will use a form of
         Clinical Trial Agreement ("CTA") form acceptable to both parties. If an
         Investigator insists upon any material changes to any provisions of the
         CTA, then Quintiles shall submit the proposed material change to
         Sponsor, and Sponsor shall review, comment on and/or approve such
         proposed changes within ten (10) working days of receipt of such
         proposed material changes. If the standard CTA form, or any changes to
         the standard CTA form approved by Sponsor, differ from the terms of
         this Agreement or a Work Order (including, but not limited to,
         provisions allowing an Investigator to publish results or data that
         Quintiles is prohibited from revealing), then Quintiles shall have no
         liability for making any such approved changes to the CTA. The parties
         acknowledge and agree that Investigators shall not be considered the
         employees, agents, or subcontractors of Quintiles or Sponsor and that
         Investigators shall exercise their own independent medical judgment.
         Quintiles' responsibilities with respect to Investigators shall be
         limited to those responsibilities specifically set forth in this
         Agreement, the applicable Work Order, and the CTA.

         If Quintiles will be paying Investigators on behalf of Sponsor, the
         parties will agree in the applicable Work Orders as to a schedule of
         amounts to be paid to Investigators. Payments for Investigators'
         services are pass-through payments to third parties and are separate
         from payments for Quintiles' Services. Such pass-through payments for
         Investigators' services shall be made by Sponsor to Quintiles in
         advance in accordance with the applicable budget and payment schedule
         for the specific Work Order. Sponsor acknowledges and agrees that
         Quintiles will not make payments to Investigators prior to receipt of
         sufficient funds from Sponsor, and that Sponsor will not withhold
         Investigator payments except to the extent that it has reasonable
         questions about the services performed by a particular Investigator.

11.0     CONFLICT OF AGREEMENTS. Quintiles represents to Sponsor that it is not
         a party to any agreement which would prevent it from fulfilling its
         obligations under this Agreement and that during the term of this
         Agreement, Quintiles agrees that it will not enter into any agreement
         to provide services which would in any way prevent it from providing
         the Services contemplated under this Agreement. Sponsor agrees that it
         will not enter into an agreement with a third party that would alter or
         affect the regulatory obligations delegated to Quintiles in any study
         or Project without the written consent of Quintiles, which will not be
         unreasonably withheld.

12.0     PUBLICATION. Project results may not be published or referred to, in
         whole or in part, by Quintiles or its affiliates without the prior
         expressed written consent of Sponsor. Neither party will use the other
         party's name in connection with any press release or marketing
         materials, without the other party's prior written consent.

13.0     REMEDIES. In addition to any other remedies available to the parties
         hereto, each party shall be entitled to seek equitable relief,
         including injunctions and specific performance,


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         in the event of a breach of the provisions of this Agreement. Neither
         party shall be entitled to, nor shall the other party, its affiliates
         or any of the other party's or its affiliates' directors, officers,
         employees, subcontractors or agents have any liability for any loss of
         profits, opportunity or goodwill, or any type of special, incidental,
         indirect or consequential damage or loss in connection with or arising
         out of this Agreement, any Work Order, or the Services performed
         hereunder. Except in circumstances involving [**], in no event shall
         the collective, aggregate liability (including, but not limited to,
         contract, negligence and tort liability) [**] or its affiliates, or
         [**] or its affiliates' directors, officers, employees, subcontractors
         and agents, under this Agreement or any Work Order hereunder [**] under
         the applicable Work Order from which such liability arose.

14.0     INDEMNIFICATION.
         (a) Sponsor shall indemnify, defend and hold harmless Quintiles and its
         affiliates, and its and their directors, officers, employees and agents
         (each, a "Quintiles Indemnified Party"), from and against any and all
         losses, damages, liabilities, reasonable attorney fees, court costs,
         and expenses (collectively "Losses"), joint or several, resulting or
         arising from any third-party claims, actions, proceedings,
         investigations or litigation relating to or arising from or in
         connection with this Agreement, any Work Order, or the Services
         contemplated herein (including, without limitation, any Losses arising
         from or in connection with any study, test, product or potential
         product to which this Agreement or any Work Order relates), except to
         the extent such Losses are determined to have resulted from the
         negligence or intentional misconduct of the Quintiles Indemnified Party
         seeking indemnity hereunder.

         (b) Quintiles shall indemnify, defend and hold harmless Sponsor and its
         affiliates, and its and their directors, officers, employees and agents
         (each, a "Sponsor Indemnified Party"), from and against any and all
         losses, damages, liabilities, reasonable attorney fees, court costs,
         and expenses (collectively "Losses"), joint or several, resulting or
         arising from any third-party claims, actions, proceedings,
         investigations or litigation relating to or arising from or in
         connection with this Agreement, any Work Order, or the Services
         contemplated herein to the extent such Losses are determined to arise
         from the negligence or intentional misconduct of a Quintiles
         Indemnified party.

15.0     INDEMNIFICATION PROCEDURE. The Indemnified Party shall give the
         Indemnifying Party prompt notice of any such claim or lawsuit
         (including a copy thereof) served upon it and shall fully cooperate
         with the Indemnifying Party and its legal representatives in the
         investigation of any matter the subject of indemnification. The
         Indemnifying Party shall be entitled at its option to control the
         defense and settlement of any claim on which it may be liable, provided
         the Indemnifying Party acts reasonably and in good faith with respect
         to all matters relating to the settlement and disposition of the claim
         to the extent such disposition or settlement relates to the Indemnified
         Party. The Indemnified Party shall not unreasonably withhold its
         approval of the settlement of any claim, liability, or action covered
         by the Indemnification provisions herein. The Indemnified Party's
         breach of any obligation hereunder will not relieve the Indemnifying
         Party's obligations


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         hereunder unless the Indemnifying Party is materially adversely
         affected by the acts or omissions of the Indemnified Party

16.0     TERMINATION.
         (a) Sponsor or Quintiles may terminate this Agreement or any Work Order
         without cause at any time during the term of the Agreement on sixty
         (60) day's prior written notice to Quintiles or Sponsor, as
         appropriate.

         (b) Either party may terminate this Agreement or any Work Order for
         material breach upon thirty (30) days' written notice specifying the
         nature of the breach, if such breach has not been substantially cured
         within the thirty (30) day period. During the 30-day cure period for
         termination due to breach, each party will continue to perform its
         obligations under the Agreement.

         (c) If either party reasonably determines, that its continued
         performance of the Services contemplated by one or more Work Orders
         would constitute a potential or actual violation of regulatory or
         scientific standards of integrity, then either party may terminate the
         applicable Work Order(s) by giving written notice stating the Work
         Order(s) being terminated and the effective date (which may be less
         than thirty days from the notice date) of such termination.

         (d) Sponsor may terminate this Agreement or any Work Order immediately
         by written notice, in the event that (i) authorization and approval to
         perform a study in the United States is withdrawn by the FDA; (ii)
         animal, human or in vitro test results, in the reasonable determination
         of Sponsor, necessitate immediate termination of a study; or (iii) the
         emergence of adverse events with a study drug or compound administered
         in a study are of such magnitude or significance that, in the
         reasonable determination of Sponsor, necessitate immediate termination.

         (e) Either party may terminate this Agreement or any Work Orders
         immediately upon provision of written notice if the other party becomes
         insolvent or files for bankruptcy. Any written termination notice shall
         identify the specific Work Order or Work Orders that are being
         terminated.

         (f) Upon any notice of termination, the parties shall promptly meet to
         discuss and coordinate the Services to be completed during the
         termination notice period ("Termination Services"). Quintiles shall
         perform such Termination Services as are reasonably necessary to either
         sustain the Studies underway pursuant to the applicable Work Order(s),
         or to accomplish an orderly wind-down of the Services, as Sponsor may
         direct. Quintiles agrees to take all commercially reasonable steps to
         minimize the costs and expenses it may incur as a result of
         termination.

         (g) Sponsor shall pay Quintiles for all Services actually performed in
         accordance with this Agreement and any applicable Work Order and
         reimburse Quintiles for all costs and expenses incurred in performing
         those Services, including all completed units or milestones and all
         non-cancelable costs incurred prior to notice of termination. In the
         event that termination is by Sponsor for cause, or as a result of
         material breach by


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         Quintiles, Sponsor may deduct from its payment obligations, amounts
         directly related to damages suffered by Sponsor as a result of the for
         cause termination. If payments are unit or milestone based, and the
         Agreement or a Work Order is terminated after costs have been incurred
         toward achieving portions of one or more incomplete units or
         milestones, Sponsor will pay Quintiles' standard fees for actual work
         performed toward those incomplete units or milestones up to the date of
         notice of termination, provided however that such payments for standard
         fees shall not exceed the payment that would have been due for a
         completed unit or milestone. Sponsor shall pay for all Termination
         Services actually performed during the termination notice period, upon
         receipt of an itemized statement from Quintiles, in accordance with
         Quintiles' standard fees and daily billing rates as specified in an
         attachment to each applicable Work Order, or as otherwise agreed by the
         parties, as well as reasonable expenses and pass-through costs
         necessary to complete activities associated with the termination of
         affected Work Orders, including the fulfillment of any regulatory
         requirements. If the total amounts pre-paid by Sponsor under any
         terminated Work Order exceed the amounts due and owing Quintiles for
         Services and Termination Services, Quintiles shall refund to Sponsor
         all such excess amounts within forty-five (45) days of the last day of
         the termination notice period.

         In addition, if the termination of any Work Order is by Sponsor
         pursuant to Section 16.0 (a) herein, or by Quintiles pursuant to
         Section 16.0 (b) herein, and [**] the Work Order [**], then Sponsor
         shall [**] associated with Termination Services, [**] as if the Project
         had continued on the timeline until Quintiles' personnel are
         re-assigned, but no longer than for a period of sixty (60) days from
         the date of notification of termination, to cover Quintiles' costs
         associated with early termination (on the basis that Quintiles shall
         have a duty to mitigate or minimize its losses).

17.0     RELATIONSHIP WITH AFFILIATES. Quintiles may use the Services of its
         corporate affiliates to fulfill Quintiles' obligations under this
         Agreement and any Work Order, provided they are included in the Work
         Order or Quintiles obtains Sponsor's prior written approval. Any
         affiliate so used shall be subject to all of the terms and conditions
         applicable to Quintiles under this Agreement or any Work Order, and
         entitled to all rights and protections afforded Quintiles under this
         Agreement and any Work Order. Quintiles agrees that Sponsor's
         affiliates may use the services of Quintiles (and its affiliates) under
         this Agreement. In such event, to the extent that Sponsor's affiliates
         elect to use the services of Quintiles in connection with a Project,
         such Sponsor's affiliates shall be bound by all the terms and
         conditions of this Agreement and the Project-related Work Order and
         entitled to all rights and protections afforded Sponsor under this
         Agreement and the Project-related Work Order. Any such affiliate of
         Sponsor or Quintiles may execute a Work Order directly. The term
         "affiliate" shall mean all entities controlling, controlled by or under
         common control with Sponsor or Quintiles, as the case may be. The term
         "control" shall mean the ability to vote fifty percent (50%) or more of
         the voting securities of any entity or otherwise having the ability to
         influence and direct the polices and direction of an entity.


Idenix Quiniles MSA                    10                           CONFIDENTIAL

<PAGE>

18.0     COOPERATION; SPONSOR DELAYS; DISCLOSURE OF HAZARDS. Sponsor shall
         forward to Quintiles in a timely manner all documents, materials and
         information in Sponsor's possession or control necessary for Quintiles
         to conduct the Services. Quintiles shall not be liable to Sponsor nor
         be deemed to have breached this Agreement or any Work Order for errors,
         delays or other consequences arising from Sponsor's failure to timely
         provide documents, materials or information or to otherwise cooperate
         with Quintiles in order for Quintiles to timely and properly perform
         its obligations. If Sponsor delays a Project from its agreed starting
         date or suspends performance of a Project for a period longer than 10
         working days, then, upon written notice from Quintiles of the delay or
         suspension, and at Sponsor's sole discretion, either: a) Sponsor will
         pay the standard daily rate of the Quintiles' personnel assigned to the
         Project and selected by Sponsor for retention on the Project, based on
         the percentage of their time allocated to the Project, for the period
         of the delay beginning on the eleventh working day, in order to keep
         the current team members; or, b) Quintiles may re-allocate the
         personnel at its discretion, and Sponsor will pay the reasonable costs,
         if any, of re-training new personnel. In addition, Sponsor will pay all
         non-cancelable costs and expenses reasonably incurred by Quintiles due
         to the delay and will adjust all timelines to reflect additional time
         required due to the delay. Sponsor shall provide Quintiles with all
         information available to it regarding known or potential hazards
         associated with the use of any substances supplied to Quintiles by
         Sponsor, and Sponsor shall comply with all current legislation and
         regulations concerning the shipment of substances by the land, sea or
         air.

19.0     FORCE MAJEURE. In the event either party shall be delayed or hindered
         in or prevented from the performance of any act required hereunder by
         reasons of strike, lockouts, labor troubles, failure of power or
         restrictive government or judicial orders, or decrees, riots,
         insurrection, war, Acts of God, severe inclement weather or other
         reason or cause beyond that party's control, then performance of such
         act shall be excused for the period of such delay, and the payment
         obligations set forth in Section 18.0 shall not accrue.

20.0     NOTICES AND DELIVERIES. Any notice required or permitted to be given
         hereunder by either party hereunder shall be in writing and shall be
         deemed given on the date received if delivered personally, on the next
         business day if sent by confirmed facsimile or by a reputable overnight
         delivery service, or three (3) days after the date postmarked if sent
         by registered or certified mail, return receipt requested, postage
         prepaid to the following addresses:

<TABLE>
         <S>                                      <C>
         If to Quintiles:                         If to Sponsor:

         Quintiles, Inc.                          Idenix Pharmaceuticals, Inc.
         5927 South Miami Boulevard               125 CambridgePark Drive
         Morrisville, North Carolina 27560-8396   Cambridge, MA 02140
         Attention: Michael P. Arlotto, Ph.D.     Attention: Deborah Lloyd
         Senior Vice President                    Associate Director, Clinical Operations
         Facsimile:                               Facsimile: (617) 250-3101
</TABLE>


Idenix Quiniles MSA                    11                           CONFIDENTIAL
<PAGE>


<TABLE>
         <S>                                            <C>
         With a copy to:

         Quintiles Transnational Legal Department       Idenix Pharmaceuticals, Inc.
         P.O. Box 13979                                 125 CambridgePark Drive
         Research Triangle Park, North Carolina         Cambridge, MA 02140
         27709-3979                                     Attention: Andrea J. Corcoran
         Attention: John Russell                        Sr. V.P., Legal & Administration
</TABLE>

         If Sponsor delivers, ships, or mails materials or documents to
         Quintiles, or requests that Quintiles deliver, ship, or mail materials
         or documents to Sponsor or to third parties, then the expense and risk
         of loss for such deliveries, shipments, or mailings shall be borne by
         Sponsor. Quintiles disclaims any liability for the actions or omissions
         of third-party delivery services or carriers.

21.0     INSURANCE. During the term of this Master Agreement, and for two (2)
         years thereafter, to cover its obligations hereunder, each party shall
         maintain insurance coverage as follows: 1) Professional Liability for
         Quintiles and Product Liability for Sponsor in amounts of at least
         US$[**]. The insured shall provide the other party with at least thirty
         (30) days prior written notice of any material change, cancellation or
         expiration of the above-required insurance.

22.0     FOREIGN CURRENCY EXCHANGE. For all Work Orders in which Quintiles will
         earn fees or incur expenses in excess of one million U.S. Dollars in a
         currency differing from the invoice and payment currency, a foreign
         currency exchange provision will be included in the Work Order.

23.0     INFLATION ADJUSTMENTS. Where services in a Work Order are provided by
         Quintiles over multiple calendar years, Quintiles may increase its fees
         at the beginning of each calendar year to reflect increases in
         Quintiles' business costs on a prospective basis only. Quintiles'
         overall costs may be increased for the next twelve (12) month period
         using the actual percentage change in the wages/earnings survey as
         published in the Economist (or as reported at www.economist.com) or the
         equivalent inflation index for each country where Services are
         performed, over the preceding twelve (12) month period.

24.0     BINDING AGREEMENT AND ASSIGNMENT. This Agreement shall be binding upon
         and inure to the benefit of Sponsor and Quintiles and their respective
         successors and permitted assigns. Either party ("Assignor") may assign
         any of its rights or obligations under this Agreement to any third
         party ("Assignee")with which it merges, affiliates or consolidates, or
         to which it transfers all or substantially all of its assets to which
         this Agreement or any Work Order relates to the extent that Assignee
         has sufficient assets and capital to reasonably satisfy Assignor's
         obligations under this Agreement or any Work Order.

25.0     WAIVER AND ENFORCEABILITY. The failure to enforce any right or
         provision herein shall not constitute a waiver of that right or
         provision. Any waiver of a breach of a provision shall not constitute a
         waiver of any subsequent breach of that provision. If any provisions
         herein are found to be unenforceable on the grounds that they are
         overly broad or in


Idenix Quiniles MSA                    12                           CONFIDENTIAL
<PAGE>

         conflict with applicable laws, it is the intent of the parties that
         such provisions be replaced, reformed or narrowed so that their
         original business purpose can be accomplished to the extent permitted
         by law, and that the remaining provisions shall not in any way be
         affected or impaired thereby.

26.0     SURVIVAL. The rights and obligations of Sponsor and Quintiles, which by
         intent or meaning have validity beyond such termination (including, but
         not limited to, rights with respect to inventions, confidentiality,
         discoveries and improvements, indemnification and liability
         limitations) shall survive the termination of this Agreement or any
         Work Order.

27.0     ARBITRATION. Any controversy or claim arising out of or relating to
         this Agreement or the breach thereof shall be settled by arbitration
         administered by the American Arbitration Association ("AAA") under its
         Commercial Arbitration Rules, and judgment on the award rendered by the
         arbitrator shall be binding and may be entered in any court having
         jurisdiction thereof. Such arbitration shall be filed and conducted at
         the office of the AAA closest to the Quintiles office having
         responsibility for the Project, and shall be conducted in English by
         one arbitrator mutually acceptable to the parties selected in
         accordance with AAA Rules. The arbitrator shall not have the power to
         award any punitive damages or any damages excluded by this Agreement.
         Either party may apply to the arbitrators for interim injunctive relief
         until the arbitration award is rendered or the dispute is otherwise
         resolved. Either Party also may, without waiving any remedy under this
         Agreement, seek from any court having jurisdiction any injunctive or
         provisional relief necessary to protect the rights or property of that
         Party pending the arbitration award.

28.0     ENTIRE AGREEMENT, HEADINGS AND MODIFICATION. This Agreement, together
         with the applicable Work Orders, contains the entire understandings of
         the parties with respect to the subject matter herein, and supersedes
         all previous agreements (oral and written), negotiations and
         discussions, except as provided in Section 1.0(d) herein. The
         descriptive headings of the sections of this Agreement are inserted for
         convenience only and shall not control or affect the meaning or
         construction of any provision hereof. Any modifications to the
         provisions herein must be in writing and signed by the parties.

         IN WITNESS WHEREOF, this Agreement has been executed by the parties
hereto through their duly authorized officers on the date(s) set forth below.

                      ACKNOWLEDGED, ACCEPTED AND AGREED TO:

QUINTILES, INC.                        INDENIX PHARMACEUTICALS, INC.

By: /s/ Michael P. Arlotto             By: /s/ Jean-Pierre Sommadossi
    ---------------------------------      -------------------------------------
               (signature)                              (signature)
Print Name: Michael P. Arlotto, Ph.D.  Print Name: Jean-Pierre Sommadossi, Ph.D.
            -------------------------              -----------------------------
Title: Senior Vice President           Title: Chief Executive Officer
       ------------------------------         ----------------------------------
Date: 2-25-2003                        Date: February 25, 2003
      -------------------------------        -----------------------------------
FEDERAL ID # 56-1323952
             ------------------------


Idenix Quiniles MSA                    13                           CONFIDENTIAL
<PAGE>


                                    EXHIBIT A
                                SAMPLE WORK ORDER

                                   WORK ORDER

         This Work Order ("Work Order") is between ____________________
("Sponsor") and _________________________ ("Quintiles") and relates to the
Master Services Agreement dated ________________________, (the "Master
Agreement"), which is incorporated by reference herein. Pursuant to the Master
Agreement, Quintiles has agreed to perform certain services in accordance with
written work orders, such as this one, entered into from time-to-time.

         The parties hereby agree as follows:

         1.       Work Order. This document constitutes a "Work Order" under the
Master Agreement and this Work Order and the services contemplated herein are
subject to the terms and provisions of the Master Agreement.

         2.       Services and Payment of Fees and Expenses. The specific
services contemplated by this Work Order (the "Services") and the related
payment terms and obligations are set forth on the following attachments, which
are incorporated herein by reference:

                  SCOPE OF WORK                         ATTACHMENT 1
                  PROJECT BUDGET                        ATTACHMENT 2
                  TIMELINE                              ATTACHMENT 3
                  PAYMENT SCHEDULE                      ATTACHMENT 4
                  TRANSFER OF OBLIGATIONS
                  (if applicable)                       ATTACHMENT 5
                  LOCAL REPRESENTATIVE DUTIES
                  (if applicable)                       ATTACHMENT 6

         3.       Term. The term of this Work Order shall commence on the date
of execution and shall continue until the services described in Attachment 1,
are completed, unless this Work Order is terminated in accordance with the
Master Agreement. If the Master Agreement is terminated or expires, but this
Work Order is not terminated or completed, then the terms of the Master
Agreement shall continue to apply to this Work Order until the Work Order is
either terminated or completed.

         4.       Affiliates and Subcontractors. Quintiles may use the services
of its corporate affiliates to fulfill Quintiles' obligations under this Work
Order, provided below or if it obtains Sponsor's prior written consent. Any such
affiliates shall be bound by all the terms and conditions of, and be entitled to
all rights and protections afforded under, the Master Agreement and this Work
Order. Any subcontractors, consultants or Quintiles' affiliates that will be
used by Quintiles in performing the Services are listed below:

         [Insert names of any subcontractors, consultants or Quintiles'
affiliates that will be used]

         5.       Amendments. No modification, amendment, or waiver of this Work
Order shall be effective unless in writing and duly executed and delivered by
each party to the other.


Idenix Quiniles MSA                    14                           CONFIDENTIAL
<PAGE>


         6.       Currency Exchange. [Insert currency exchange provision in all
Work Orders in which Quintiles will earn fees or incur expenses in excess of one
million U.S. Dollars in a currency differing from the invoice and payment
currency]

         7.       Inflation and Cost Adjustment. [Insert cost adjustment
provision and inflation provision, if appropriate.]

                      ACKNOWLEDGED, ACCEPTED AND AGREED TO:

[Quintiles]                             [Sponsor]

By:                                     By:
   ---------------------------------       -------------------------------------

Title:                                  Title:
      ------------------------------          ----------------------------------

Date:                                   Date:
     -------------------------------         -----------------------------------










Idenix Quiniles MSA                    15                           CONFIDENTIAL

<PAGE>


                                    EXHIBIT B
                  SAMPLE LOCAL REPRESENTATIVE DUTIES ATTACHMENT

                                [To be provided]
<PAGE>


                                    EXHIBIT C

                            SAMPLE CHANGE ORDER FORM

Change Order Number: _____________ Agreement No.: ______________________________

Customer:_________________________________ Quintiles Project Code: _____________

Customer Contact: ________________________

Date of Change Notification Form approval by Customer
(if applicable):________________________________________________________________

Project Name:___________________________________________________________________

Protocol Number(s):_____________________________________________________________

Description and/or date of original agreement:__________________________________

Quintiles Project Manager: _______________ Date of Change Order: _______________

Description of Change Order:



Costs Associated with Change Order:



Does this change the overall timeline?
         [ ] Yes*  [ ] No  [ ] N/A
         *If yes, revised timeline attached.

Does this change the Transfer of Obligations from Customer to Quintiles?
         [ ] Yes*  [ ] No  [ ] N/A
         *If yes, please attach revised Transfer of Obligations.

Does this change in scope necessitate a revision to the payment schedule?
         [ ] Yes*  [ ] No  [ ] N/A
         *If yes, revised payment schedule attached.

Does this change in scope necessitate a revision to any local representative
designation?
         [ ] Yes*  [ ] No  [ ] N/A
         *If yes, revised local representative attachment is attached.

BUDGET SUMMARY:

--------------------------------------------------------------------------------
ITEM                           EFFECTIVE DATE              AMOUNT
--------------------------------------------------------------------------------
Original Contract
--------------------------------------------------------------------------------
Change Order No. 1
--------------------------------------------------------------------------------


Idenix Quiniles MSA                    19                           CONFIDENTIAL
<PAGE>


--------------------------------------------------------------------------------
Change Order No. 2, etc.
--------------------------------------------------------------------------------
Total Revised Contract
--------------------------------------------------------------------------------

                      AGREED TO, ACKNOWLEDGED, AND ACCEPTED

QUINTILES, INC.                           [CUSTOMER NAME]


-------------------------------------     --------------------------------------
Signature                                 Signature

-------------------------------------     --------------------------------------
Name (print)                              Name (print)

-------------------------------------     --------------------------------------
Title                                     Title

-------------------------------------     --------------------------------------
Date                                      Date











Idenix Quiniles MSA                    20                           CONFIDENTIAL