EXHIBIT 10.1

WHEREVER CONFIDENTIAL INFORMATION IS OMITTED HEREIN (SUCH OMISSIONS ARE
DENOTED BY AN ASTERISK), SUCH CONFIDENTIAL INFORMATION HAS BEEN SUBMITTED
SEPARATELY TO THE SECURITIES AND EXCHANGE COMMISSION PURSUANT TO A REQUEST
FOR CONFIDENTIAL TREATMENT

                               LICENSING AGREEMENT

         This Agreement is made as of SEPTEMBER 30, 1999 between CHIRHOCLIN INC.
("CRC"), a Maryland corporation with offices at 15500 Gallaudet Avenue, Silver
Spring, MD 20905-4176 and REPLIGEN INC. ("Repligen"), a Delaware corporation,
with offices at 117 Fourth Avenue, Needham, MA 02494.

                                    RECITALS
         WHEREAS, CRC is engaged in development of synthetic secretin products
for marketing under the Federal Food, Drug, and Cosmetic Act ("FFDC Act"), and
is the beneficial owner of the INDs and NDAs for the Product(s) (as defined
below); and
         WHEREAS, Repligen desires to commercially market the Product(s) and for
that purpose CRC is willing to grant a license to Repligen, on the terms and
conditions set out below;
         NOW, THEREFORE, CRC and Repligen do hereby agree as follows:

1.       DEFINITIONS
         The following expressions have the following meanings:
         1.1      "Competitive Product" means any product which is competitive
                  either with Repligen Secretin Product(s) for treatment of
                  autism or with Product(s), but does not include changes in the
                  use or formulation of the Product(s) in accordance with
                  Paragraph 12.
         1.2      "Competitor" means anyone engaged in the development of a
                  Competitive Product as defined herein.
         1.3      "IND" means an Investigational New Drug application made to
                  the U.S. Food and Drug Administration ("FDA") in support of
                  the marketing of a drug for human use.
         1.4      "NDA" means a New Drug Application made to the U.S. Food and
                  Drug Administration ("FDA") in support of the marketing of a
                  drug for human use.
         1.5      "NDA Approval" means the combination of: (1) receipt of final
                  approval from the FDA to market the Product(s) and (2) the
                  accompanying grant of market exclusivity via Orphan Drug
                  Status for the Product(s).
         1.6      "Net Revenue" means the gross revenue received from Product
                  sales minus the fully loaded, i.e. direct and indirect, costs
                  attributable to the manufacturing, marketing, distribution,
                  and sales of the Product(s), * .
         1.7      "Product(s)" means either or both of pSecretin and hSecretin.
         1.8      "hSecretin" means that form of synthetic human secretin
                  developed and clinically evaluated by CRC under its INDs and
                  NDAs.
         1.9      "pSecretin" means that form of synthetic porcine secretin
                  developed and clinically evaluated by CRC under its INDs and
                  NDAs.
         1.10     "Therapeutic Applications" means the treatment or prevention
                  of any human disorder with the exception of *.
         1.11     "Repligen Secretin Products" means synthetic human secretin
                  drug substances and finished, formulated, manufactured
                  products developed independently of CRC by Repligen for
                  Therapeutic Applications.
         1.12     "Orphan Drug Status" means the grant of seven years of
                  marketing exclusivity for a Product pursuant to the Orphan
                  Drug Act of 1983.
         1.13     *.

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2.       GRANT OF LICENSES
         2.1      CRC grants to Repligen, and Repligen hereby accepts, for the
                  duration of this Agreement and subject to the conditions of
                  this Agreement and in accordance with Paragraphs 12 and 14, a
                  sole and exclusive worldwide license and right to use, market
                  and sell the Product(s) for uses outside of Therapeutic
                  Applications.
         2.2      CRC grants to Repligen, and Repligen hereby accepts, for the
                  duration of this Agreement and subject to the conditions of
                  this Agreement and in accordance with Paragraphs 11 and 12 an
                  exclusive option to negotiate an exclusive royalty-bearing
                  license under a separate agreement to commercialize the
                  Product(s) for Therapeutic Applications. During the term of
                  the Agreement, CRC will not offer any third party a license to
                  commercialize the Product(s) under any terms.
         2.3      During the term of this Agreement, CRC will not develop or
                  market any Competitive Product.
         2.4      During the term of this Agreement, Repligen will not develop
                  or market new products that are competitive with Product(s)
                  for diagnostic and * indications.
         2.5      During the term of this Agreement, Repligen will not
                  sublicense any rights which it may hold under this Agreement
                  without CRC's prior written approval, such approval not to be
                  unreasonably withheld.
         2.6      During the term of this Agreement, CRC will not sublicense any
                  rights which it may hold under this Agreement without
                  Repligen's prior written approval, such approval not to be
                  unreasonably withheld.
3.       TERM
         3.1.     This Agreement shall become effective on October 1, 1999.
                  Unless terminated earlier pursuant to Paragraph 4, the initial
                  term of this Agreement shall be from the effective date until
                  the later to occur of: 1) October 1, 2009, or 2) the
                  expiration of marketing exclusivity of the last indication for
                  which Orphan Drug Status has been granted subject to this
                  Agreement including any expansion of Orphan Drug Status
                  authorized under Paragraph 12; but may be extended thereafter
                  by mutual agreement according to Paragraph 3.2.
         3.2      In the event that this Agreement is not terminated pursuant to
                  Paragraph 4 prior to its expiration, it may be renewed after
                  its expiration upon written agreement of the Parties.
         3.3      Following termination, Repligen will own the trademark and
                  vial and carton artwork for Product(s) and CRC will own those
                  NDAs which relate to diagnostic and *
                  indications and may market the Product(s) under its own
                  trademark for diagnostic indications and, if approved, for
                  ERCP pancreatitis.
         3.4      Twelve (12) months prior to the expiration date as defined by
                  Paragraph 3.1 of this Agreement, each Party must notify the
                  other in writing of its intent to extend or renew the term of
                  the Agreement.

4.       TERMINATION
         4.1      This Agreement shall terminate upon the expiration of the term
                  under Paragraph 3, unless earlier terminated pursuant to
                  Paragraph 4.2, 4.3, or 4.8 hereof.
         4.2      CRC may, at its option, terminate this Agreement upon:
                  4.2.1    failure, inability, or refusal by Repligen to perform
                           any term, covenant, or condition of this Agreement,
                           which failure, inability, or refusal shall continue
                           for sixty (60) days following written notice thereof
                           by CRC specifying such default
                  4.2.2    sale or transfer of a controlling interest of stock
                           or assets of Repligen to a Competitor of CRC without
                           the prior written approval of CRC;
                  4.2.3.   the insolvency of Repligen; an assignment by it for
                           the benefit of creditors; or, unless vacated or
                           withdrawn within sixty (60) days of the filing or
                           appointment thereof, the filing of a petition in
                           bankruptcy by or against Repligen, or the appointment
                           of a receiver or trustee of any part of Repligen's
                           business;
                  4.2.4.   the assignment by Repligen of this Agreement, or any
                           rights hereunder, without CRC's prior written
                           approval; or
                  4.2.5.   delinquency of Repligen in making payments for
                           Product(s) sold under this Agreement or other
                           payments due hereunder, which delinquency is not
                           cured within sixty (60) days of receiving notice of
                           such delinquency from CRC.
                  4.3.     Repligen may, at its option, terminate this Agreement
                           upon:

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                  4.3.1.   failure, inability, or refusal by CRC to perform any
                           term, covenant, or condition of this Agreement, which
                           failure, inability, or refusal shall continue for
                           sixty (60) days following written notice thereof by
                           Repligen, specifying such default;
                  4.3.2.   sale or transfer of a controlling interest of stock
                           or assets of CRC to a Competitor of Repligen without
                           the prior written approval of Repligen;
                  4.3.3.   the insolvency of CRC; an assignment by it for the
                           benefit of creditors; or, unless vacated or withdrawn
                           within sixty (60) days of the filing or appointment
                           thereof, the filing of a petition in bankruptcy by or
                           against CRC, or the appointment of a receiver or
                           trustee of any part of CRC's business;
                  4.3.4.   the assignment by CRC of this Agreement, or any
                           rights hereunder, without Repligen's prior written
                           approval;
         4.4.     Notwithstanding the foregoing, either Party shall have the
                  right to waive the application of any of the foregoing events
                  of termination by written notification to the other.
         4.5.     Upon termination of this Agreement in accordance with
                  Paragraph 4.1 or 4.2, Repligen will no longer have rights to
                  market the Product(s), and will at CRC's direction return
                  remaining Product(s) to CRC for appropriate disposition.
         4.6.     In the event that this Agreement is terminated by Repligen in
                  accordance with Paragraph 4.3 prior to the occurrence of any
                  NDA Approval, CRC hereby agrees to return within one year to
                  Repligen any and all payments made under Paragraph 7. In the
                  event of such termination, if Product has been purchased by
                  Repligen according to Paragraph 14.4, Repligen will return
                  said Product to CRC and CRC will reimburse Repligen for the
                  cost of its purchase.
         4.7.     In the event that this Agreement is terminated by Repligen in
                  accordance with Paragraph 4.3 following an NDA Approval, CRC
                  hereby agrees that: 1) Repligen will have the right to recover
                  all payments made under Paragraph 7 from CRC's share of Net
                  Revenues, 2) Repligen will retain all rights granted under
                  Paragraphs 2 and 8 of this Agreement up until such time as all
                  payments made under Paragraph 7 have been recovered by
                  Repligen, 3) during the period following such termination up
                  until such time as all payments made under Paragraph 7 are
                  recovered by Repligen from CRC's share of Net Revenues,
                  Repligen's share of Net Revenues pursuant to Paragraph 8 will
                  continue to flow to Repligen, 4) CRC, its heirs, assigns,
                  and/or successors, shall provide any and all rights and
                  enablements required in order to permit Repligen to continue
                  to market and sell Product(s) without interruption or
                  restriction during the period following such termination up
                  until such time as all payments made under Paragraph 7 are
                  recovered, and 5) after all payments made under Paragraph 7
                  are recovered by Repligen all rights granted under this
                  Agreement will revert to CRC.
         4.8.     From October 1, 1999 up    * following the date of submission
                  to the FDA of the NDA for hSecretin, Repligen shall have the
                  right to terminate this Agreement unilaterally, thereby
                  relinquishing all Product rights granted hereunder. In the
                  event that Repligen terminates the Agreement according to this
                  Paragraph 4.8, Repligen shall have the right to recover any
                  and all payments made under Paragraph 7. If termination
                  according to this Paragraph 4.8 occurs prior to NDA Approval,
                  CRC shall return said payments made under Paragraph 7 within
                  one year of the date of such termination. If termination
                  occurs following NDA Approval, CRC will transfer all Net
                  Revenues to Repligen until such time as the total of all Net
                  Revenues transferred equals the payments made by Repligen
                  under Paragraph 7.
         4.9      For the purposes of Paragraphs 4.6, 4.7, and 4.8 herein,
                  payments made by Repligen under Paragraph 7 shall include both
                  cash payments and stock granted. In the event of termination
                  pursuant to any of Paragraphs 4.6, 4.7, and 4.8 and in
                  addition to the return of any cash payments, CRC shall return
                  to Repligen any unsold stock and shall repay to Repligen the
                  face value at time of grant of any stock sold.

5.       REVERSION OF RIGHTS
         5.1      If, * years following NDA Approval of pSecretin, Repligen
                  has failed to obtain FDA approval to commercialize a Repligen
                  Secretin Product; the rights to Product(s) will revert to CRC,
                  and CRC may terminate this Agreement. Notwithstanding the
                  foregoing, Repligen will retain rights to any trademarks and
                  artwork it has obtained for the Product(s).

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6.       TERRITORY
         6.1      Repligen is authorized to market the Product(s) worldwide for
                  diagnostic and * indications, provided, that
                  all necessary marketing authorization shall be registered in
                  the name of CRC or one of its subsidiaries. Such
                  authorizations shall be pursued with the written approval of
                  CRC under terms mutually agreeable to the Parties.
         6.2      Notwithstanding the above subparagraph, no Product(s) and
                  unapproved versions thereof produced outside the United States
                  may be imported and marketed in the United States by Repligen,
                  its subsidiaries, affiliates, or permitted assigns without the
                  prior written consent of CRC.

7.       PAYMENTS
         7.1.     CRC receives licensing/milestone payments from Repligen
                  totaling * according to the following schedule:




                              UPFRONT                                     CASH          STOCK
                                                                               
                  Upon execution of License Agreement                 $1,000,000

                             MILESTONES
                  pSecretin NDA Approval                               *

                  The earlier to occur of: 1) FDA Approval of *                     * shares
                  or 2) six (6) months following * NDA Approval
                  FDA Approval of  *                                   *
                  hSecretin NDA Approval                               *


                  Unless otherwise instructed by CRC, Repligen shall make cash
                  payments via electronic wire transfer to the following
                  address:

                  Chevy Chase Bank
                  15777 Columbia Pike
                  Burtonsville, MD 20866

                  Bank ABA or Routing Number: *
                  Customer's Account Number: *
                  Customer's Account Title: ChiRhoClin Inc., in care of
                  Edward D. Purich

         7.2      The stock may not be resold for one year following issue after
                  which it may be sold under the provisions of Rule 144 (17
                  C.F.R.ss.230.144).
         7.3.     This Agreement is made in reliance upon CRC's express
                  representations that 1) the shares of Repligen Common Stock to
                  be issued to CRC hereunder (the "Shares") are for CRC's own
                  account for the purpose of investment and not with a view to,
                  or for sale in connection with, the distribution thereof, nor
                  with any present intention of distributing or selling the
                  Shares, 2) the Shares will not be sold without registration
                  under the Securities Act of 1933, as amended (the "Securities
                  Act"), or an exemption therefrom, such as Rule 144 as
                  promulgated under the Securities Act, 3) CRC prior to the
                  purchase of the Shares has had the opportunity to ask
                  questions of and receive answers from representatives of
                  Repligen concerning the finances, operations and business of
                  Repligen, and 4) CRC is capable of evaluating the merits and
                  risks of the purchase of the Shares and can afford a complete
                  loss of its investment. Until such time as the Shares shall
                  have been registered under the Securities Act, or shall have
                  been transferred in accordance with an opinion of counsel
                  satisfactory to Repligen that such registration is not
                  required, stop transfer instructions shall be issued to
                  Repligen's transfer agent, and the certificates representing
                  the Shares shall bear a legend substantially as follows:
                  "The shares represented by this certificate have not been
                  registered under the Securities Act of 1933 or applicable
                  state securities laws. These shares have not been acquired
                  with a view to distribution or resale, and may not be sold,
                  mortgaged, pledged, hypothecated or otherwise without an
                  effective registration statement for such shares under the
                  Securities Act of 1933 and any applicable state securities
                  laws, or an opinion of counsel satisfactory to

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                  Repligen that registration is not required under the
                  Securities Act of 1933 or under applicable state securities
                  laws."
                  CRC further understands and acknowledges that Repligen is
                  under no obligation to register the Shares under the
                  Securities Act.
         7.4      CRC will maintain diligent efforts to obtain NDA Approval for
                  both pSecretin and hSecretin and will use best efforts to
                  complete the preparation of the NDA for hSecretin prior to *.
         7.5      The shares shall be duly authorized, validly issued and
                  non-assessable shares of common stock of Repligen.


8.       ROYALTIES
         8.1      Royalties on Products will be paid by Repligen to CRC on
                  the basis of Net Revenue received from Product sales and
                  according to the following schedule:



     --------------------------------------------------------------------------- ------------------------------------
     Phase                                                                       Revenue Share
     --------------------------------------------------------------------------- ------------------------------------
                                                                              
     First * of Net Revenue                                                      *


     Second * of Net Revenue                                                     *


     Thereafter, until FDA approval of a Repligen Secretin Product               *


     Following FDA approval of a Repligen Secretin Product and up until the      *
     expiration of market exclusivity for Products                               of Net Revenues for last year
                                                                                 prior to FDA approval of a
                                                                                 Repligen Secretin Product, or,
                                                                                               *
                                                                                 of diagnostic and *
                                                                                 use (such volume of use to be
                                                                                 determined according to
                                                                                 Paragraph 8.2), whichever is higher
     --------------------------------------------------------------------------- ------------------------------------


         8.2      Following expiration of marketing exclusivity via Orphan Drug
                  Status for Product(s), so long as Repligen has received NDA
                  approval for its own secretin product for autism; Repligen
                  will pay CRC a royalty which is * of the calculated net
                  revenues based solely on the diagnostic sale of Product(s),
                  such diagnostic sale volume to be determined according to a
                  mutually agreeable third party source.

9.       REPRESENTATIONS AND WARRANTIES
         9.1.     CRC hereby represents and warrants that it is entitled to the
                  property rights necessary to enable it to grant to Repligen
                  the license referred to herein and that it is the sole and
                  exclusive owner of said rights.
         9.2.     CRC will use its best efforts to obtain from the FDA IND and
                  NDA approval for the Product(s). Notwithstanding any other
                  provision in this Agreement to the contrary, delay in
                  obtaining IND or NDA approval for the Product(s) which is not
                  attributable to lack of diligence by CRC shall not be grounds
                  for termination by Repligen.
         9.3.     CRC will use its best efforts to ensure that all Product(s)
                  manufactured and supplied to Repligen pursuant to this
                  Agreement conforms to manufacturing specifications. CRC
                  reserves the right at any time to make changes in any aspect
                  of the composition, appearance, or formulation of Product(s)
                  as long as: 1) Repligen has had six months prior notification
                  of such changes and has approved such changes such approval
                  not to be unreasonably withheld, and

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                  2) they are in compliance with all applicable FDA
                  requirements. CRC at its sole discretion and without prior
                  notification of Repligen may make changes to the manufacturing
                  process which are intended solely for the removal or reduction
                  of impurities. In the event that CRC makes any such changes,
                  CRC will promptly advise Repligen in writing of the respects
                  in which the new Product(s) will differ, if at all, from the
                  then-marketed Product(s).
         9.4.     CRC will use its best efforts to ensure that manufacturing of
                  Product(s) designated for U.S. marketing complies with FDA's
                  requirements relating to current Good Manufacturing Practices
                  (cGMPs) and any other applicable federal or state regulations
                  and guidelines.
         9.5.     Repligen will use its best efforts to ensure that Product(s)
                  designated for U.S. marketing comply with FDA promotion and
                  labeling requirements for human drug products.

10.      CONFIDENTIALITY
         10.1.    During the term of this Agreement, The Parties agree to
                  strictly abide by the terms of the Confidentiality Agreement,
                  executed August 4, 1999, and attached hereto as APPENDIX 1.

11.      IND/NDA PRODUCT DEVELOPMENT

         11.1.    CRC will have full operational and financial responsibility
                  for obtaining, and will use best efforts to obtain, NDA
                  Approval for Product(s) for: 1) diagnosis of a) pancreatic
                  exocrine function, b) pancreatic cancer through a procedure
                  for obtaining desquamated pancreatic cells for histopathologic
                  examination, and c) gastrinoma; and 2) * which will include,
                  without limitation, best efforts to complete activities
                  according to APPENDIX 2. At the request of Repligen, CRC
                  will, with appropriate prior notification, afford qualified
                  representatives of Repligen the right to review the
                  hSecretin NDA package, including regulatory correspondence,
                  prior to NDA Approval for hSecretin. Once each year following
                  FDA submission of the hSecretin NDA, CRC will, with
                  appropriate prior notification, afford qualified
                  representatives of Repligen the right to review all material
                  correspondence with regulatory authorities regarding the
                  aforesaid indications to assure ongoing compliance with
                  regulatory requirements.
         11.2.    CRC will own the INDs and the approved NDAs for Product(s) and
                  will have ongoing responsibility for manufacturing and
                  regulatory affairs with respect to said INDs and NDAs. In the
                  event and to the extent that CRC fails or is unable to carry
                  out or fulfill such responsibilities, CRC, its heirs, assigns,
                  and successors, hereby agree to provide for and/or to Repligen
                  any and all means as may be required in order to allow such
                  fulfillment.
         11.3.    CRC agrees *. CRC and Repligen will identify a mutually
                  acceptable alternative contractor for the bulk drug substance
                  manufacture of pSecretin and hSecretin and will use best
                  efforts to complete at least one production lot of each prior
                  to March 31, 2000. Repligen will participate in the assessment
                  of the second manufacturer's cGMP capabilities and may perform
                  testing of said production lots. During the term of the
                  Agreement, Repligen will have the right to review the QC and
                  QA batch records related to product release testing and its QA
                  group may audit the manufacturing contractors for general
                  facility related cGMP and regulatory compliance.
         11.4.    No new clinical studies of Product(s) in Therapeutic
                  Applications will be initiated by Repligen after the signing
                  of this Agreement unless the Parties mutually agree on such
                  initiation. At such time as Repligen and CRC agree to initiate
                  a new clinical study of Product(s) in a Therapeutic
                  Application, the Parties will negotiate a separate exclusive
                  license agreement for the use of Product(s) in said
                  Therapeutic Application. CRC will then provide Repligen with
                  the right to reference its relevant INDs and Repligen will
                  file its own IND and conduct said new study. Repligen
                  acknowledges that CRC has an ongoing clinical study of
                  Product(s) in * in non-autistic patients that will remain
                  under the exclusive control of CRC.
         11.5     CRC will keep Repligen fully informed on matters relating to
                  NDA Approval. In the event that deficiencies are identified in
                  the NDA, Repligen may, at its option, participate in the NDA
                  Approval process for the purpose of assisting CRC in remedying
                  the deficiencies, in which case Repligen will have the right
                  to recover its costs from CRC's share of Product(s) revenues.

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12       EXPANSION OF PRODUCT APPROVAL
         12.1.    With respect to new diagnostic applications, CRC will use best
                  efforts to gain additional approval and expanded Orphan Drug
                  Status for the Product(s). Administration and financing of
                  these efforts will be the responsibility of CRC.
                  12.1.1.  In the event that CRC elects not to pursue expanded
                           approval for a new diagnostic application, Repligen
                           may proceed under terms mutually agreeable to the
                           Parties.
                  12.1.2.  Sharing of the revenues received from the expanded
                           approval will be the same as for previously approved
                           diagnostic indications following the reimbursement of
                           those costs (plus interest) incurred by Repligen as
                           in Paragraph 8.

13.      PATENTS
         13.1.    In the event that CRC obtains rights to any patents or patent
                  applications that relate to the composition of, method of use,
                  or process for producing secretin, Repligen shall have a first
                  option to negotiate an exclusive royalty-bearing license to
                  such rights for Repligen Secretin Product, said option to
                  extend for the term of this Agreement. Insofar as Repligen may
                  require a license to such rights in order to market and sell
                  Product(s), such license shall be automatically granted and
                  shall be royalty free.
                  13.1.1.  The royalty rate to be paid by Repligen to CRC
                           pursuant to said license will be negotiated between
                           the Parties and become the subject of a separate
                           agreement. Said royalty rate shall in any case be
                           generally consistent with industry standards.
                  13.1.2.  The sale volume upon which royalties will be due will
                           be based upon that fraction of total sales that are
                           covered by valid claims in the licensed CRC patents
                           as determined according to a mutually agreeable third
                           party source.

14.      MARKETING OPERATIONS
         14.1     Marketing and promotional activities including Product(s)
                  pricing will be mutually agreed in writing in a draft
                  marketing plan prior to November 30, 1999, said plan to be
                  revised and updated by the Parties as needed but at least once
                  annually thereafter.
         14.2     Repligen will have the sole right to authorize the
                  distribution of Product(s) for all current clinical studies of
                  Product(s) in Therapeutic Applications and CRC will promptly
                  share with Repligen all results received from such clinical
                  studies. To the extent that CRC has the right to publicly use
                  safety data from such studies, the Parties agree to use such
                  data as appropriate to support marketing activities.
         14.3     Following FDA approval of Repligen's Secretin Product, CRC
                  will cease and desist from any and all activities related to
                  the marketing and sale of Product(s) for Therapeutic
                  Applications if any such activities are ongoing.
         14.4     Repligen will purchase from CRC a mutually agreed upon
                  inventory of launch stock of the Product(s) and will fund any
                  mutually agreed upon marketing activities that precede the NDA
                  Approval. These costs will be reimbursed from initial gross
                  revenues prior to the revenue split as described in Paragraph
                  8.
         14.5     Annual budgets related to each aspect of operations will be
                  prepared by the responsible Party and will be reviewed and
                  approved by the other Party. Any deviation from such budget
                  will require the prior approval of the other Party. The total
                  expenses of the Parties related to the cost of manufacture,
                  marketing, distribution, and sales of Product(s) shall not
                  exceed * of the gross revenues without prior mutual approval.
         14.6     Distribution of Product(s) will be accomplished as specified
                  in the mutually agreed upon marketing plan and revenues will
                  flow through Repligen. Royalties due to CRC will be reconciled
                  on a quarterly basis by Repligen. Estimated payments based on
                  actual revenues received by Repligen from the sale of
                  Product(s) will be paid to CRC monthly in the first year
                  following NDA Approval following which payments will be made
                  quarterly on the basis of actual revenues.
         14.7     CRC shall have the right once during each calendar year to
                  inspect, or have an agent, accountant or other representative
                  inspect, during normal business hours, and upon reasonable
                  advance notice (not less than 14 days), such books, records
                  and other supporting data of Repligen as may be necessary to
                  verify Repligen's computation of royalties due under this

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                  Agreement. CRC agrees to maintain the confidentiality of any
                  information acquired during such inspection or review. Failure
                  to permit an inspection or audit upon receipt of proper notice
                  is grounds for breach of this Agreement.
         14.8     The Parties will work together to develop a plan to maximize
                  revenues worldwide.

15.      SUPPLY OF PRODUCT
         15.1     Following the execution of this Agreement, the Parties agree
                  to, by December 31, 1999, negotiate and enter into a separate
                  agreement which will govern the supply and transfer of
                  Product(s) by and between the Parties. Said agreement shall
                  include, without limitation: placing and filling of orders for
                  bulk drug substance and drug product, transfer pricing (if
                  applicable), and control and ownership of inventory through
                  the manufacturing and distribution chain, as well as a general
                  plan for minimizing the cost of goods prior to distribution.

16.      PRODUCT BRANDING
         16.1     Repligen may at its option market pSecretin under its own
                  brand name, trade name, trademark, or logo or under a brand
                  name, trade name, trademark, or logo owned by CRC. For all
                  other Product(s), Repligen may market the Product(s) under its
                  own brand name, trade name, trademark or logo, but may not
                  market the Product(s) under any brand name, trade name,
                  trademark or logo owned by CRC, or any name which is a
                  colorable imitation of, or is likely to be confused with, any
                  names or logos owned by CRC, except as authorized in writing
                  by CRC. Following termination of this Agreement, CRC may
                  market the Product(s) under its own brand name, trade name,
                  trademark or logo, but may not market the Product(s) under any
                  brand name, trade name, trademark or logo owned by Repligen,
                  or any name which is a colorable imitation of, or is likely to
                  be confused with, any names or logos owned by Repligen, except
                  as authorized in writing by Repligen.
         16.2     Subject to subparagraph 16.1, trade names of Product(s) and
                  all aspects of artwork and design for vial and carton labels
                  for Product(s) will be owned and controlled exclusively by
                  Repligen. CRC will have right of review of said artwork and
                  design to the extent it is required for the maintenance of
                  regulatory compliance.

17.      PUBLICITY
         17.1.    Press releases related to the announcement of this Agreement
                  and to NDA Approval as well as any press releases related to
                  Therapeutic Applications of Product(s), with the exception of
                  *, will be initiated by Repligen and will originate from
                  Repligen except as specified herein. CRC will have the right
                  of prior review and comment on such press releases to insure
                  accurate representations of subject matter and CRC's
                  contribution.
         17.2     CRC will take the lead on joint release of information related
                  to diagnostic and * applications of Product(s). Repligen will
                  have the right of prior review and comment on such press
                  releases.

18.      FORCE MAJEURE
         18.1     The obligation of the Parties hereunder shall be suspended by
                  the occurrence of such unforeseeable events beyond the control
                  of the Parties as acts of God, war, mobilization, riot,
                  sabotage, explosion, fire or other casualty, a generalized and
                  nation-wide inability to obtain suitable and sufficient
                  materials, or law or regulation restricting performance,
                  provided, however, that each Party shall take reasonable
                  measures to remove the disability and resume operation at the
                  earliest possible date.

19.      INDEMNITY
         19.1     Repligen agrees to defend, indemnify, and hold CRC harmless
                  from and against any claim, liability, loss, cost, or expense
                  (including reasonable counsel fees) in connection with any
                  claims, suits, actions, demands, or judgments arising out of,
                  or in connection with, or relating in any manner to, this
                  Agreement which are attributable to the negligence or reckless
                  or willful activities of Repligen, its officers, employees,
                  contractors, and agents.
         19.2     CRC agrees to defend, indemnify, and hold Repligen harmless
                  from and against any claim, liability, loss, cost, or expense
                  (including reasonable counsel fees) in connection with any

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                  claims, suits, actions, demands, or judgments arising out of,
                  or in connection with, or relating in any manner to, this
                  Agreement which are attributable to the negligence or reckless
                  or willful activities of CRC, its officers, employees,
                  contractors, and agents.

20.      INSURANCE
         20.1     Each Party agrees to carry comprehensive General Liability
                  Insurance (including Directors and Officers Liability coverage
                  and Products Liability coverage) with coverage limits as set
                  forth in Appendix 3. The coverage limits shall be reviewed
                  annually by the Parties, and if appropriate, adjusted by
                  mutual agreement of the Parties. Such policies shall be
                  carried with responsible insurers and shall specifically
                  recognize and insure the covered Party against its contractual
                  liability hereunder. Certificates of such insurance shall be
                  furnished to each Party and shall provide for at least sixty
                  (60) days' written notice to a Party of the cancellation or
                  any material modification thereof.

21.      NOTICES
         21.1     Any notice or communication under or in connection with this
                  Agreement shall, unless otherwise provided herein, be in
                  writing and shall be delivered personally, or by post, telex,
                  cable, or facsimile to the addresses given in this Agreement
                  or at such other address as the recipient may have notified to
                  the other party in writing.
         21.2     A notice or other communication shall be deemed effective, in
                  the case of a letter, on the third day after posting, or, in
                  the case of a telex, cable, or facsimile, on the day
                  immediately following the date of dispatch (other than a
                  Saturday, Sunday, or bank holiday).
         21.3     Where delivery of any notice or communication is by post,
                  delivery shall be by first-class mail, postage prepaid,
                  addressed to the respective parties as follows:

                           TO REPLIGEN:
                           Walter C. Herlihy, Ph.D.
                           President, Chief Executive Officer
                           Repligen Inc.
                           117 Fourth Avenue
                           Needham, MA 02494

                           TO CRC:
                           Edward D. Purich, Ph.D.
                           Chief Executive Officer
                           ChiRhoClin Inc.
                           15500 Gallaudet Avenue
                           Silver Spring, MD 20905-4176

         21.4     Where delivery of any notice or communication is by telex,
                  cable, facsimile, or other electronic method, such notice or
                  communication shall also be sent promptly by first-class mail,
                  as described in subparagraph 21.3 above. Failure to send such
                  notice by mail shall not, however, render the earlier
                  electronic notice ineffective, unless such notice is
                  demonstrably illegible.

22.      ARBITRATION

         22.1     The Parties agree that in the event a dispute arises out of or
                  relating to this Agreement, the Parties shall attempt in good
                  faith to resolve the dispute through discussion and
                  alternative dispute resolution according to the following
                  procedure.
                  22.1.1   Good Faith Discussion - The complaining Party shall
                           notify the other Party of the dispute. All involved
                           Parties shall attempt to discuss the dispute in good
                           faith.
                  22.1.2   Arbitration - Should the dispute remain unresolved
                           after good faith discussion for sixty (60) days after
                           the notice under subparagraph 22.1.1 above, the
                           Parties agree to arbitrate under the rules of
                           conciliation and arbitration of the American
                           Arbitration Association ("AAA"). There shall be three
                           arbitrators, one being selected by Repligen and one
                           being selected by CRC, and the third being selected
                           by the two arbitrators so

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                           selected. If a Party fails to nominate an arbitrator
                           within 15 days from the date of the notification made
                           to it of the other Party's request for arbitration,
                           or if the two arbitrators fail within 15 days from
                           the date of their appointment to reach agreement on
                           the third arbitrator, then the third arbitrator shall
                           be appointed in accordance with the AAA rules. The
                           place of arbitration shall be in New York City, New
                           York. The arbitration expenses shall be paid by the
                           losing party. If the arbitrators do not find for one
                           party's position in its entirety, then the Parties
                           shall share the arbitration expenses equally between
                           the Buyer and the Sellers. The Parties shall also be
                           responsible for their own expenses, including
                           attorney fees.
                  22.1.3   Enforceability - This Agreement, including the
                           arbitration provision in subparagraph 22.1.2 above
                           and any award, shall be enforceable in any federal or
                           state court in the United States.
                  22.1.4   Miscellaneous - The Parties waive the defense of
                           inconvenient forum and lack of personal jurisdiction
                           in any proceeding brought in federal or state court
                           in New York City, New York to enforce the arbitration
                           provision in subparagraph 22.1.2 above. Further, the
                           Parties agree that notice under this Agreement shall
                           constitute acceptable and valid service of process
                           for all proceedings to enforce the arbitration
                           provision of subparagraph 22.1.2 above.

23.      MISCELLANEOUS
         23.1     This instrument and the Appendices hereto constitute the
                  entire Agreement between the Parties, supersede all prior or
                  contemporaneous representations, understandings, or
                  agreements, and shall not be extended, varied, modified, or
                  supplemented except by an agreement in writing and signed by
                  the Party to be charged.
         23.2     The headings used herein are for ease of reference only and
                  are not to be used in the interpretation or construction of
                  this Agreement.
         23.3     The prevailing Party in any arbitration or litigation
                  involving this Agreement shall be entitled to recover its
                  costs and reasonable counsel fees, in addition to any other
                  remedy or relief to which it may be entitled.
         23.4     Neither Party shall have the right to assign this Agreement or
                  any interest therein without the prior written consent of the
                  other. Such consent shall not be unreasonably withheld.
         23.5     Repligen shall at all times be, and remain, an independent
                  contractor and not an agent, partner, or joint venturer of CRC
                  for any purpose whatsoever and shall have no authority to
                  create or assume any obligation, express or implied, in the
                  name of, or on behalf of, CRC, or to bind it in any manner
                  whatsoever.
         23.6     The failure of either Party to enforce at any time, or for any
                  period of time, any one or more of the provisions hereof,
                  shall not be construed to be a waiver of such provisions or of
                  the right of such Party thereafter to enforce each such
                  provision.
         23.7     If any provision of this Agreement shall be held invalid under
                  any applicable law, such invalidity shall not affect any other
                  provision of this Agreement.
         23.8     This Agreement shall be binding upon, and inure to the benefit
                  of, the Parties hereto, their successors, and permitted
                  assigns.
         23.9     This Agreement shall be construed in accordance with the laws
                  of the Commonwealth of Massachusetts, without regard to
                  applicable statutes or rules regarding conflicts of laws.
         23.10    This Agreement may be executed in counterparts by any of the
                  Parties hereto on two counterparts, each of which shall be
                  deemed an original, but both of such respective counterparts
                  shall together constitute one and the same Agreement.
         [SIGNATURES FOLLOW]

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IN WITNESS WHEREOF, the Parties have caused this Agreement to be duly executed
as of the day and year first above written.

CHIRHOCLIN INCORPORATED             REPLIGEN INCORPORATED



By /s/ Edward D. Purich                         By: /s/ Daniel P. Witt
   --------------------------------                 -------------------------
         Edward D. Purich, Ph.D.                Daniel P. Witt
         Chief Executive Officer                Vice President

Date: September 30, 1999                        Date: September 30, 1999
      --------------------                            ------------------





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