EXHIBIT 10.1

                                SUPPLY AGREEMENT

This agreement ("Agreement") is made as of May 26, 1999, by and between Repligen
Corporation ("REPLIGEN"), a Delaware corporation with principal offices at 117
Fourth Ave., Needham, MA 02494 and Amersham Pharmacia Biotech AB ("BIOTECH"), a
corporation incorporated in Sweden with principal offices at Bjorkgatan 30,
SE-751 84 Uppsala (each a "Party" and collectively "the Parties").

      WHEREAS, REPLIGEN possesses capabilities relating to the large scale
      manufacture of recombinant proteins including protein A; and

      WHEREAS, BIOTECH utilizes a proprietary form of recombinant protein A in a
      variety of products marketed and sold by BIOTECH; and [*]

      WHEREAS, the Parties wish to enter a long term relationship wherein
      REPLIGEN will be the preferred manufacturer of recombinant protein A for
      BIOTECH's use.

      NOW THEREFORE, for the mutual covenants contained herein, and for other
      good and valuable considerations, the Parties agree as follows:

1.    DEFINITIONS

      For the purpose of this Agreement, the terms set forth hereunder shall be
      defined as follows:

      a.    "Biotech IPA" means those forms of immobilized Biotech rPA which are
            manufactured, marketed, and sold to the general public by BIOTECH as
            further described in Appendix A attached hereto.

      b.    "Biotech rPA" means that form of unimmobilized recombinant protein A
            which is proprietary to BIOTECH.

      c.    "Biotech Specifications" means that set of physical, chemical, and
            functional characteristics that are reported in the Certificate of
            Analysis, attached hereto as Appendix B. Biotech Specifications may
            be modified from time to time by mutual agreement of the Parties.


                                       19

[*] indicates material which has been omitted and for which confidential
treatment has been requested. All such material has been filed with the
Commission pursuant to rule 24b-2 promulgated under the Securities Exchange Act
of 1934, as amended.


      d.    "Confidentiality Agreement" shall mean that confidentiality
            agreement dated April 20, 1998 entered into by and between the
            Parties.

      e.    "New Product" means that product described in Appendix D.

      f.    "First Agreement" means that agreement made by and between the
            Parties on September 29, 1992.

      g.    "License Agreement" means that agreement between the Parties made
            effective on the execution date of this Agreement in which REPLIGEN
            grants to BIOTECH i) a non-exclusive license to US Patent No.
            5,084,559 ("Protein A Domain Mutants") and ii) a license to
            technology, know-how, and certain other rights relating to New
            Product.

       h.   "Process Technology" means any and all know-how, proprietary
            materials and reagents, documentation, trade secrets, and technology
            relating to the production of Biotech rPA.

       i.   "Repligen rPA" means those forms of unimmobilized recombinant
            protein A which are proprietary to REPLIGEN.

      j.    "Master Agreement" means that agreement made by and between the
            Parties and dated December 17, 1998.

      k.    "Contract Year" means each calendar year during the term of the
            Agreement.

      l.    "Article(s)" shall mean either or both of Biotech rPA and New
            Product produced by REPLIGEN for BIOTECH under this Agreement.

2.    MANUFACTURING

      a.    During the term of this Agreement, REPLIGEN agrees to manufacture
            Biotech rPA in compliance with the Biotech Specifications and those
            documented processes or any modification thereto to which the
            Parties may mutually agree and to supply it to BIOTECH according to
            the terms and conditions herein.

      b.    During the term of this Agreement, REPLIGEN agrees to manufacture
            New Product in compliance with the documented procedures developed
            by REPLIGEN and to supply it to


                                       20


            BIOTECH according to the terms and conditions of this Agreement and
            the License Agreement.

      c.    Any and all subcontractors engaged by REPLIGEN to carry out any
            aspect of the manufacture of Biotech rPA will be bound by a
            confidential disclosure agreement ("CDA") with terms and conditions
            substantially similar to the Confidentiality Agreement. BIOTECH will
            have the right to consent to all subcontractors involved in
            manufacture of Biotech rPA which consent shall not be unreasonably
            withheld. Following consent by BIOTECH and execution by the
            subcontractor of a CDA, REPLIGEN may share Process Technology with
            such party. BIOTECH may not contact REPLIGEN's sub-contractors with
            specific reference to the manufacture of Biotech rPA without the
            prior consent of REPLIGEN. REPLIGEN may utilize alternative
            facilities under its control in the manufacture of Biotech rPA.
            REPLIGEN will give BIOTECH nine (9) months prior written notice of
            any intended change in facility or sub-contractor for approval by
            BIOTECH, such approval not to be unreasonably withheld by BIOTECH.

      d.    From time to time, BIOTECH may request that reasonable changes be
            made in the process used by REPLIGEN to manufacture Biotech rPA and
            REPLIGEN agrees to use best efforts to incorporate such changes. In
            the event that requested changes may effect the cost of production,
            the Parties shall agree on new firm prices prior to the
            implementation of said change.

      e.    REPLIGEN shall inform BIOTECH nine (9) months in advance of any
            changes which it may wish to make in the process used to manufacture
            Biotech rPA or any major changes which it may wish to make in the
            process used to manufacture New Product and BIOTECH shall have
            ninety (90) days to approve such change, such approval not to be
            unreasonably withheld. If BIOTECH cannot approve such change,
            REPLIGEN agrees to continue to supply Biotech rPA and/or New Product
            as manufactured by the mutually agreed upon process.

      f.    Changes to any aspect of the manufacturing process for New Product
            which are not considered to constitute a major


                                       21


            process change may be made at any time by mutual agreement of the
            Parties.


      g.    REPLIGEN represents that it possesses the resources required
            including personnel, machinery and premises, to meet its obligations
            under the terms of this Agreement in all material respects provided
            that BIOTECH complies with its obligations under this Agreement.

3.    PURCHASE AND SALE OF PRODUCT

      a.    During the term of this Agreement, BIOTECH agrees to purchase and
            REPLIGEN agrees to sell Biotech rPA and New Product according to the
            terms and conditions set forth herein.

      b.    During each Contract Year, BIOTECH intends to purchase from REPLIGEN
            and REPLIGEN agrees to maintain the ability to manufacture for
            BIOTECH no less than [*] of BIOTECH's total requirements for Biotech
            rPA. In any Contract Year in which BIOTECH does purchase [*] of said
            annual requirements from REPLIGEN, REPLIGEN shall be considered to
            be the preferred supplier ("Preferred Supplier") to BIOTECH for
            Biotech rPA.

      c.    BIOTECH shall purchase a minimum quantity of New Product from
            REPLIGEN during the first Contract Year, i.e. calendar 1999,
            according to the following schedule:

                [*]
                [*]

            as well as such additional quantities which it may elect to
            purchase.

      d.    Within 20 days following the completion of each quarter of a
            Contract Year, BIOTECH will inform REPLIGEN as to the status of: i)
            the inventory of Biotech rPA and Biotech IPA on hand as well as the
            aggregate quantity of Biotech IPA that has been sold during the
            preceding quarter, ii) the inventory of New Product on hand, and
            iii) the total quantities of BIOTECH rPA ordered from third party
            suppliers in said preceding quarter. REPLIGEN will have the right to
            audit all relevant records of BIOTECH with respect to this
            information, however BIOTECH shall have no


                                       22

[*] indicates material which has been omitted and for which confidential
treatment has been requested. All such material has been filed with the
Commission pursuant to rule 24b-2 promulgated under the Securities Exchange Act
of 1934, as amended.


            obligation to reveal the terms or conditions of any arrangements
            regarding third parties.

4.    PRODUCT PRICING

      a.    The price paid by BIOTECH to REPLIGEN for all Biotech rPA purchased
            during the first Contract Year, i.e. calendar 1999, will be
            according to the schedule set forth in Appendix C:

      b.    The price for Biotech rPA purchased by BIOTECH from REPLIGEN in each
            Contract Year after the first year of the Agreement will be based
            upon the price schedule in Appendix C and adjusted on the basis of
            the average yield obtained in the previous year according to the
            following formula:

               [*]

            wherein average yield is the average yield obtained over all
            manufacturing runs carried out in the immediately preceding calendar
            year of production.

      c.    The price paid to REPLIGEN by BIOTECH for New Product under the
            Agreement will be as set forth in Appendix C:

      d.    On or before October 31 of each Contract Year, the Parties will
            agree upon new, firm pricing for the subsequent Contract Year based
            upon: i) any price reduction based on yield according to this
            Section 4b herein, ii) any change in the United States Consumer
            Price Index as published at the end of the third quarter of the
            preceding calendar year or some other index or indices as may be
            mutually agreed upon by the parties, and iii) any other factors,
            such as justifiable and documented changes in REPLIGEN's cost of
            manufacture, altered market conditions, process modifications, etc.
            The new, firm prices will be made effective as of January 1 of the
            following Contract Year and will remain in effect throughout said
            Contract Year. In the event that the Parties cannot agree on any
            price changes, the prices shall remain unchanged for the following
            Contract Year.


                                       23

[*] indicates material which has been omitted and for which confidential
treatment has been requested. All such material has been filed with the
Commission pursuant to rule 24b-2 promulgated under the Securities Exchange Act
of 1934, as amended.


5.    ORDERS, FORECASTS, AND PAYMENT

      a.    On or before September 30, 1999 and thereafter prior to the end of
            each calendar quarter while this Agreement is in force BIOTECH shall
            deliver a written rolling forecast by quarter of its estimated need
            of Articles during the coming twelve-month period, stating Article
            numbers, and quantities with reasonable detail. This forecast will
            provide a basis for REPLIGEN's resource planning with regard to
            component and materiel procurement and production capacity. The
            first, third, and fourth quarterly forecast within each rolling
            twelve-month forecast shall be non-binding upon either of BIOTECH
            and REPLIGEN. The forecast for the second quarter within each
            rolling twelve-month forecast ("Set Quarter") will have certain
            binding obligations upon each of the Parties with respect to said
            second quarter, as set forth in this Section 5 hereunder. Once the
            forecast which establishes a Set Quarter has been received by
            REPLIGEN, it shall not be changed except by mutual agreement of the
            Parties.

      b.    Commencing January 1, 2000 (i.e. the first Set Quarter to occur
            under this Agreement) and thereafter throughout the term of the
            Agreement, BIOTECH shall, from time to time and as it deems
            appropriate, issue written, binding purchase orders to REPLIGEN,
            stating the Article number, quantity, shipping destination, and
            shipping date for each Article. Shipping for international
            destinations shall be solely on Mondays. The stated shipping date
            shall be based on the agreed lead time. Lead time is defined as the
            number of days from the date on which BIOTECH issues the order until
            the date on which product is delivered by REPLIGEN according to
            Section 6 herein.

      c.    In each Set Quarter during the term of the Agreement, REPLIGEN
            agrees to deliver to BIOTECH with a two week lead time up to one
            hundred-fifty percent (150%) of the quantity of Articles forecast
            for that Set Quarter. If, in any Set Quarter, REPLIGEN does not
            deliver Articles up to said 150% of that forecast according to said
            two week lead time, BIOTECH is entitled to reduce the price paid for
            such Articles by 1% for each week of delay up to a maximum of 10%.

      d.    For quantities of Articles ordered by BIOTECH in any Set Quarter
            that exceed 150% but do not exceed 200% of the


                                       24


            amount forecasted for that Set Quarter, REPLIGEN shall make best
            efforts to deliver said quantities with a lead time of six (6)
            weeks. If, in any Set Quarter, REPLIGEN does not deliver Articles in
            excess of 150% but less than 200% of that forecast according to said
            six week lead time, BIOTECH is entitled to reduce the price paid for
            such Articles by 1% for each week of delay up to a maximum of 10%.
            For any quantities of Articles ordered by BIOTECH in any Set Quarter
            that exceed 200% of the amount forecasted for that Set Quarter,
            REPLIGEN shall have no obligation to meet prescribed lead time for
            shipping with respect to those excess quantities. REPLIGEN shall,
            however, in all cases use reasonable efforts to adhere to a two week
            lead time, to keep BIOTECH informed as to expected shipping dates,
            and to supply BIOTECH with such excess quantities as promptly as
            possible.

      e.    In the event of the occurrence of Force Majeure or any other event
            beyond the reasonable control of REPLIGEN which results in the
            inability of REPLIGEN to deliver Articles according to prescribed
            lead times of this Section 5, REPLIGEN's sole obligations hereunder
            shall be: i) to give BIOTECH prompt notice of said event in writing
            and ii) to seek diligently to deliver such Articles at the earliest
            opportunity.

      f.    [*] of the forecast for each Set Quarter shall be binding upon
            BIOTECH with respect to purchase of Articles in that quarter. Prior
            to the last Monday of any quarter in which BIOTECH has failed to
            submit purchase orders that total [*] of the amount which was
            forecast for that quarter when it was a Set Quarter, REPLIGEN shall
            request that an order be placed by BIOTECH for such quantity of
            Articles as represents the difference between the quantity of
            Articles ordered for that quarter to date and the amount of Articles
            binding on BIOTECH for that Set Quarter. In response to such
            request, BIOTECH agrees to place a purchase order in respect of such
            quantity prior to the end of said Set Quarter.

      g.    Nothing in any purchase order submitted by BIOTECH or invoice or
            order acknowledgment submitted by REPLIGEN pursuant to this
            Agreement shall be construed as superseding or amending the terms of
            this Agreement absent


                                       25

[*] indicates material which has been omitted and for which confidential
treatment has been requested. All such material has been filed with the
Commission pursuant to rule 24b-2 promulgated under the Securities Exchange Act
of 1934, as amended.


            written agreement by the other Party which specifically references
            this Agreement.

      h.    Payment shall be made in full, in US dollars, thirty (30) days after
            invoice. Invoices shall be sent upon delivery of the Articles

      i.    If BIOTECH fails to make timely payment, REPLIGEN shall be entitled
            to charge interest on the aggregate amount of the overdue payment
            commencing on the due date at a rate equal to the current discount
            rate set by the US Federal Reserve Board plus five (5) percentage
            points.

      j.    Within three (3) days of receipt of a purchase order for Articles,
            REPLIGEN shall inform BIOTECH as to when delivery should be made.
            REPLIGEN shall further inform BIOTECH at that time as to whether any
            delay in delivery may be expected.

6.    DELIVERY, SHIPPING, AND TITLE

      a.    Delivery shall be made as FCA, Repligen, 117 Fourth Ave. Needham, MA
            as defined by Incoterms.

      b.    The ownership, right to possession, title to and all risk of loss of
            all Articles shall pass to BIOTECH at the time of delivery.

7.    OTHER OBLIGATIONS

      a.    For any Contract Year in which REPLIGEN is the Preferred Supplier
            under this Agreement, BIOTECH's obligation to pay royalties to
            REPLIGEN under the First Agreement shall be waived and no royalties
            shall be due.

      b.    For any Contract Year in which REPLIGEN does not achieve Preferred
            Supplier status due to a failure on the part of BIOTECH to submit
            purchase orders to REPLIGEN, royalties under the First Agreement
            will be retroactively due on all product sales which occurred during
            that Contract Year according to terms of the First Agreement. Such
            royalties shall be due and payable in full within 90 days of the end
            of any Contract Year in which REPLIGEN is not the Preferred Supplier
            due to the failure of BIOTECH to submit purchase orders.


                                       26


      c.    For any Contract Year in which REPLIGEN does not achieve Preferred
            Supplier status due to a failure on the part of REPLIGEN to deliver
            Biotech rPA in response to purchase orders from BIOTECH, BIOTECH's
            obligation to pay royalties to REPLIGEN under the First Agreement
            shall be waived and no royalties shall be due.

8.    SECURITY STOCK AND DISASTER PLAN

      a.    As part of a comprehensive disaster plan and commencing upon April
            1, 2000, REPLIGEN will maintain a security stock of [*] of Biotech
            rPA, to be stored under controlled and documented conditions at
            Livingston Health Care, 220 Lake Street, Newark, DE 19702 or an
            equivalent facility(s) designated by Repligen. This security stock
            will be turned over on an annual basis.

      b.    Within two months of the signing of this Agreement, REPLIGEN and
            BIOTECH hereby agree to establish and set in place a detailed action
            plan for how REPLIGEN will handle obligations under the Agreement in
            case of a disruption of production due to such events as Force
            Majeure or due to such similar events not within REPLIGEN's control.
            The Parties agree that the establishment, implementation, and/or
            maintenance of such disaster plan shall not result in significant
            additional costs for REPLIGEN. The basic elements of the disaster
            plan will consist of:

                  o     maintenance of a security stock by REPLIGEN

                  o     identification and qualification of a second
                        fermentation subcontractor before the end of the second
                        Contract Year

                  o     plan for transfer of purification/finishing within a six
                        (6) week time frame to an alternative facility for a
                        period of up to six (6) months in the event that
                        REPLIGEN's facility becomes incapacitated

      c.    The presentation of such action plan shall not in any event be
            interpreted as to affect BIOTECH's rights to


                                       27

[*] indicates material which has been omitted and for which confidential
treatment has been requested. All such material has been filed with the
Commission pursuant to rule 24b-2 promulgated under the Securities Exchange Act
of 1934, as amended.


            other remedies in case of REPLIGEN's breach of the Agreement.

9.    QUALITY ASSURANCE, CERTIFICATES, AND INSPECTIONS

      a.    REPLIGEN shall establish and maintain a quality assurance system
            which, after being approved by BIOTECH, will enable REPLIGEN to
            issue a Certificate of Analysis (CoA) showing that delivered
            Articles are conforming to the Biotech Specifications. BIOTECH is
            prepared to accept Articles received as complying with the Agreement
            and with this CoA.

      b.    All Articles delivered by REPLIGEN to BIOTECH shall conform to the
            Biotech Specifications and such conformance shall be documented by a
            CoA. Articles delivered by REPLIGEN to BIOTECH shall also be in
            compliance with all testing which may be required by the agreed and
            documented procedures, this Agreement, and applicable law. All
            testing procedures shall be in accordance with those documented
            quality control procedures developed by the Parties in connection
            with the process developed and approved by the Parties. REPLIGEN
            shall accompany each shipment of Articles with a CoA evidencing that
            the Article being shipped has passed all purity, quality control,
            and other tests required hereunder.

      c.    With reasonable prior notice to REPLIGEN and at BIOTECH's sole
            expense, BIOTECH is entitled to inspect and observe REPLIGEN's
            manufacture of Articles, to audit REPLIGEN's quality control and
            inspection procedures, and to have access to all data from such
            control of the Article and to take samples and make such other
            investigations as BIOTECH deems necessary. REPLIGEN shall reserve
            the right for BIOTECH to perform such inspections on the premises of
            subcontractors engaged by REPLIGEN, such inspections to be scheduled
            by REPLIGEN following reasonable prior notice by BIOTECH and to be
            carried out jointly by representatives of both Parties and at the
            sole expense of BIOTECH. BIOTECH's right of inspection under this
            head shall not diminish REPLIGEN's obligation to deliver Articles
            which comply with the specifications of this Agreement.

10.   WARRANTY


                                       28


      a.    Except as otherwise agreed in writing, REPLIGEN warrants that: i)
            the Articles delivered to BIOTECH under this Agreement shall be
            manufactured and tested in accordance with the documented
            procedures, ii) the Articles will conform to the CoA, iii) the
            requirements under this Agreement will have been performed and
            satisfied, and iv) title to Articles will pass to BIOTECH free and
            clear of all liens, charges, and encumbrances save for those which
            occur pursuant to this Agreement (Warranty). This Warranty shall
            survive receipt of the Articles by BIOTECH for twelve (12) months in
            the case of Biotech rPA and for eighteen (18) months in the case of
            New Product and no claim for a breach of this warranty may be
            brought after the end of the applicable period. Except as otherwise
            agreed by REPLIGEN in writing, the foregoing Warranty sets forth
            REPLIGEN's sole and exclusive representations with respect to
            Articles sold to BIOTECH under this Agreement. BIOTECH's remedies
            under this Warranty shall be limited to the replacement of
            non-conforming Articles according to the terms and conditions of
            this Section 10 with REPLIGEN bearing the cost of shipping and
            insurance. The foregoing Warranty shall not apply to defects
            resulting from misuse, negligence, or accident on the part of
            BIOTECH or any third party.

      b.    Following notification by BIOTECH that any Articles are
            non-conforming under the Warranty, replacement under the Warranty
            shall be made as follows:

                  i.    REPLIGEN shall ship requested Articles to BIOTECH within
                        five (5) days of receipt of the replacement request from
                        BIOTECH at no cost for BIOTECH at such time.

                  ii.   Within five (5) days of any replacement request, BIOTECH
                        shall ship a sample of the non-conforming Articles to
                        REPLIGEN and REPLIGEN shall complete comparative testing
                        between said non-conforming sample and an archived
                        sample from the same lot of Articles. If this
                        comparative testing demonstrates that both the
                        non-conforming sample and the archived sample do not
                        conform to the CoA, the Parties agree that the
                        replacement under i. falls under the Warranty. If,
                        however, REPLIGEN


                                       29


                        determines that the archived sample is conforming to the
                        CoA, and REPLIGEN can make it likely that the
                        non-conformance of the Articles replaced is due to
                        BIOTECH's handling of said Articles or other
                        circumstances outside of REPLIGEN's control, BIOTECH
                        will pay for the replacement Articles in full.

                  iii.  The quantity of Biotech rPA replaced under the Warranty
                        in any quarter shall be limited to [*]. The quantity of
                        New Product replaced under the Warranty in any single
                        quarter shall be limited to [*]. Replacement of Articles
                        under the Warranty may be made from security stock
                        maintained pursuant to this Agreement.

      c.    The Parties agree that the Warranty with respect to Biotech rPA is
            based on good faith estimates of expected minimum stability under
            defined storage conditions and that stability tests will be
            performed by BIOTECH and REPLIGEN to confirm these estimates. Such
            stability tests will be completed no later than December 31, 2000
            and will be used by the Parties to establish a Warranty period for
            the remaining term of the Agreement, which may be different than 12
            months. The Parties agree that there is no reason to differentiate
            the Warranty periods for Biotech rPA and New Product.

      d.    If REPLIGEN has made any replacements of Biotech rPA under the
            Warranty according to the provisions of Section 10.b.i. and
            stability testing conducted according to Section 10.c. indicates
            that the non-conformance leading to such replacement occurred as a
            result of instability under controlled storage conditions, BIOTECH
            shall immediately reimburse REPLIGEN as if such replacement had been
            a new sale of Biotech rPA.

11.   TERM AND TERMINATION

      a.    This Agreement will remain in effect from the date of signing until
            December 31, 2008 unless terminated earlier according to the
            provisions of this Section 11.

      b.    Either Party may terminate this Agreement upon the material breach
            of the other Party's performance pursuant


                                       30

[*] indicates material which has been omitted and for which confidential
treatment has been requested. All such material has been filed with the
Commission pursuant to rule 24b-2 promulgated under the Securities Exchange Act
of 1934, as amended.


            to either of this Agreement or the Master Agreement, upon 90 days
            written notice. The failure to cure such breach to the other Party's
            satisfaction within 90 days will result in the immediate termination
            of this Agreement.

      c.    In the event that BIOTECH issues no purchase orders to REPLIGEN for
            Biotech rPA in any two consecutive Contract Years, REPLIGEN may
            terminate this Agreement.

12.   COLLABORATION

      a.    The Parties agree to cooperate with each other and to act in good
            faith in carrying out the purpose and intent of this Agreement.
            Toward that end Parties agree to meet twice each year in the first
            two Contract Years and thereafter once during each Contract Year to
            analyze results achieved and to take joint action to achieve good
            results for both. The site for such meetings will alternate between
            REPLIGEN's place of business in Needham, MA and BIOTECH's place of
            business in Uppsala, Sweden or such other location as may be
            mutually agreed by the Parties.

13.   INFRINGEMENT

      a.    REPLIGEN shall indemnify and hold harmless BIOTECH, its associated
            companies and its customers from every claim, lawsuit or action
            alleging that the use or maintenance of any Article constitutes
            infringement of a patent, copyright or other intellectual right
            except in the instance where the infringement is a direct
            consequence of a method, design or other instruction furnished by
            BIOTECH for manufacture of the Article. During the term of this
            Agreement, each Party further agrees not to make any claim for
            intellectual rights against the other Party or in respect of a
            customers' use or maintenance of BIOTECH rPA, BIOTECH IPA, or
            REPLIGEN rPA.

      b.    If a judgment or injunction concerning infringement has been entered
            which: 1) prohibits or prevents any further use or maintenance of an
            Article by BIOTECH, and 2) is not a direct consequence of a method,
            design, or other


                                       31


            instruction furnished by BIOTECH for the manufacture of the Article;
            REPLIGEN shall at BIOTECH's request and at its own expense use best
            efforts to either:

                  (i)   replace or provide another equivalent Article, the use
                        of which does not to REPLIGEN's knowledge constitute an
                        infringement, or

                  (ii)  modify the Article so that it no longer constitutes to
                        REPLIGEN's knowledge an infringement or violates the
                        judgment or order, provided that such modification does
                        not affect the function of the Article or its
                        compatibility with the end product.

            The provisions of this Subsection 13b shall not apply to Articles
            which have been modified, adapted or otherwise altered by BIOTECH.

       c.   If either Party learns that an infringement exists or is possible as
            a result of use of an Article, the other Party shall be informed as
            soon as possible.

14.   PRODUCT LIABILITY

      a.    With respect to Articles manufactured under this Agreement, REPLIGEN
            agrees to carry product liability insurance, for a total coverage of
            $2 million dollars, to cover claims which may be made against
            BIOTECH and/or REPLIGEN as a result of hazardous defects occurring
            in such Articles.

      b.    Upon request from BIOTECH, REPLIGEN shall produce proof of product
            liability insurance coverage. In the event that BIOTECH requests
            that REPLIGEN increase its insurance coverage, the Parties will
            immediately negotiate an adjustment to the price of the Articles
            accordingly.

15.   GROUNDS FOR EXEMPTION

      a.    The following circumstances constitute grounds for exemption insofar
            as they render compliance with the Agreement impossible or unduly
            onerous (Force Majeure):


                                       32


            Labor dispute and every other circumstance over which the Parties
            have no control, such as fire, war, mobilization or unforeseen
            callup to military service of comparable extent, requisition,
            confiscation, currency restrictions, revolts and riots, scarcity of
            means of transportation, general scarcity of goods and limited
            availability of motive power, as well as deficiencies and delays in
            delivery of goods from subcontractors caused by such exempting
            circumstances.

      b.    It is incumbent upon a Party who wishes to cite Force Majeure to
            inform the other Party without delay when the relevant circumstances
            have arisen and when they have ceased to prevail.

      c.    If compliance with the Agreement is delayed for more than six (6)
            months by Force Majeure as specified in Subsection 15a above, either
            Party shall be entitled to terminate the Agreement by giving thirty
            days prior written notice to the other Party.

16.   GENERAL

      a.    This Agreement is not assignable by either Party absent the other
            Party's written consent. If REPLIGEN is purchased by a third party
            which is a competitor of BIOTECH, BIOTECH has the right to approve
            the transfer of the Agreement. For purposes hereof, the term
            "purchase" shall mean i) a sale of all or substantially all of the
            assets of REPLIGEN or ii) the merger and consolidation of REPLIGEN
            with or into another corporation such that the stockholders of
            REPLIGEN immediately following such transaction hold, directly or
            indirectly, less than 50% of the voting securities of the
            corporation surviving such transaction.

      b.    Any and all information disclosed by one Party to the other under
            this Agreement shall be handled in accordance with the terms and
            conditions of the Confidentiality Agreement and consequently be
            treated as confidential - as agreed therein - for the duration of
            the Agreement and for a period of five (5) years thereafter.


                                       33


      c.    Any changes or amendments to this Agreement shall be in writing and
            made by mutual agreement of the Parties.

      d.    REPLIGEN will not sell or transfer Biotech rPA to any party other
            than BIOTECH, except with BIOTECH's consent.

      e.    During the term of the Agreement, BIOTECH will supply REPLIGEN with
            any and all requested quantities of chromatography media which are
            marketed and sold by BIOTECH and required by REPLIGEN in the
            manufacture of Biotech rPA at a [*] discount to the then current
            list price.

      f.    Sepharose 4FF which is used specifically in the manufacture of New
            Product for BIOTECH under this Agreement will be provided to
            REPLIGEN at no cost. At the time of signing of this Agreement,
            BIOTECH will repurchase from REPLIGEN up to 100 liters of Sepharose
            4FF at the invoice price paid by REPLIGEN, said Sepharose 4FF to be
            used solely for the manufacture of New Product.

      g.    This Agreement is subject to and shall be construed and enforced in
            accordance with the laws of the State of New York. Any disputes
            arising hereunder shall be resolved with reference to the English
            language version of this Agreement regardless of any translations
            made for the convenience of the Parties. All disputes between the
            Parties shall be resolved by binding arbitration in accordance with
            the rules and regulations of the American Arbitration Association in
            the city of New York, NY. Notwithstanding anything herein to the
            contrary, the Parties acknowledge and agree that each shall have the
            right to obtain equitable relief against the other provided that
            each Party hereby agrees to submit to the jurisdiction of the courts
            of the State of New York or the federal courts of the United States
            located in New York and that the venue for all such proceedings
            shall lie in the State of New York.

IN WITNESS WHEREOF, the Parties hereto have hereunto set their hands and seals
and duly executed this Agreement the day and year first written above.


FOR REPLIGEN CORPORATION                    FOR AMERSHAM PHARMACIA
                                            BIOTECH AB

 /s/ Daniel P. Witt                            /s/ Arne Forsell




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[*] indicates material which has been omitted and for which confidential
treatment has been requested. All such material has been filed with the
Commission pursuant to rule 24b-2 promulgated under the Securities Exchange Act
of 1934, as amended.



/s/ Daniel P. Witt                                   /s/ Arne Forsell
- --------------------------------------------------------------------------------
Name                                                 Name

VP, Business Development                             President
- --------------------------------------------------------------------------------
Title                                                Title

May 26, 1999                                         June 27,1999
- --------------------------------------------------------------------------------
Date                                                 Date


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