<PAGE>

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


                                                                 Exhibit 10.29


                              DEVELOPMENT AGREEMENT

                                       for

                   AFFINITY CHROMATOGRAPHY PURIFICATION MEDIA

THIS AGREEMENT,  effective as of September 29, 1997 (the "Effective Date"), is
made by and between DYAX CORP., a Delaware corporation ("DYAX"),  and GENETICS
INSTITUTE, INC. a Delaware corporation  ("CUSTOMER").

WHEREAS DYAX possesses technology and expertise related to the discovery of
proteins and peptides having novel binding properties and the development and
manufacture of affinity chromatography purification media for use in the
separation and purification of proteins;

WHEREAS CUSTOMER is engaged in the discovery, development and manufacture of
************* ("Customer Product");

WHEREAS DYAX and CUSTOMER wish to enter into a collaboration in which DYAX will
utilize its technology and expertise to develop for CUSTOMER a unique affinity
ligand and chromatography purification media (the "Dyax Product") for use by
CUSTOMER in the purification of Customer Product.

NOW, HEREBY the parties do hereby agree as follows:

                           ARTICLE 1. DISCOVERY PHASE

1.1. Conduct of Discovery Phase. DYAX agrees to devote commercially reasonable
resources and efforts to the diligent conduct of the work described in the
Discovery Phase section of the Work Plan Outline included in Exhibit 1 attached
hereto. The Discovery Phase shall commence on the Effective Date and is expected
to continue for a period of *************. The Discovery Phase shall end when
DYAX has delivered to CUSTOMER the Discovery Phase Deliverables described in the
Work Plan Outline. During the Discovery Phase, DYAX's Project Director shall
meet with representatives of CUSTOMER at the reasonable request of CUSTOMER to
respond to questions and facilitate the exchange of appropriate information on
the progress of the Discovery Phase. In addition, Dyax shall submit a quarterly
summary progress report to CUSTOMER and a final written report as set forth in
the Work Plan Outline.
<PAGE>

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

1.2. Discovery Phase Payments. In consideration of the rights granted to
CUSTOMER herein and undertaking the Discovery Phase, CUSTOMER agrees to pay DYAX
************* of execution of this Agreement.

1.3. Initiation of the Development Phase. ************* following its receipt of
the Discovery Phase Deliverables, CUSTOMER shall notify DYAX in writing of
whether it intends to proceed to the Development Phase of the collaboration.
Prior to the initiation of work under the Development Phase, DYAX and CUSTOMER
shall negotiate in good faith any modifications to the Development Phase section
of the Work Plan Outline set forth in Exhibit 1 attached hereto and any
resulting change to the Development Phase payments, and the relevant provisions
of Exhibit 1 and Article 2 shall be amended accordingly by written agreement.

                          ARTICLE 2. DEVELOPMENT PHASE

2.1. Conduct of Development Phase. If CUSTOMER elects to proceed to the
Development Phase, DYAX agrees to devote commercially reasonable resources and
efforts to the diligent conduct of the work described in the Development Phase
section of the Work Plan Outline included in Exhibit 1 attached hereto, as such
section may be amended in accordance with Section 1.3 of this Agreement. The
Development Phase is expected to continue for a period of ************* and
shall end when DYAX has delivered to CUSTOMER the Development Phase Deliverables
described in the Development Phase Section of the Work Plan Outline, as such
section may be amended in accordance with Section 1.3 of this Agreement. During
the Development Phase, DYAX's Project Director shall meet with representatives
of CUSTOMER at the reasonable request of CUSTOMER to respond to questions and
facilitate the exchange of appropriate information on the progress of the
Development Phase. In addition, DYAX shall submit a quarterly summary progress
report to CUSTOMER and a final written report as set forth in the Work Plan
Outline.

2.2. Development Phase Payments.

      (a) In consideration of the performance by DYAX of the Development Phase,
CUSTOMER agrees to pay DYAX ************* for each Dyax Product candidate for
which DYAX is to initiate Development Phase work., payable with the written
notification pursuant to Section 1.3 of this Agreement or upon completion of any
negotiations entered into in accordance with such Section, whichever is later.
In the event CUSTOMER desires DYAX to expand the Development Phase
*************, CUSTOMER agrees to pay DYAX in advance ************* for each
additional *************; and

      (b) CUSTOMER further agrees to pay DYAX *************, payable within 30
days of the occurrence of the delivery by DYAX of the first ************* which
meets the Milestone requirements for the Development Phase set forth in the Work
Plan Outline.

      2.3 Initiation of the Optimization Phase. Within 60 days following its
receipt of the Development
<PAGE>

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

Phase Deliverables described in Exhibit 1, CUSTOMER shall notify DYAX in writing
of whether it intends to proceed to the Optimization Phase of the collaboration.
Prior to the start of work under the Optimization Phase, DYAX and CUSTOMER shall
negotiate in good faith an Optimization Phase section to be set forth in an
expanded Work Plan Outline and shall agree upon the Optimization Phase payments,
and Exhibit 1 and Article 3 of this Agreement shall be amended accordingly by
written agreement.

                          ARTICLE 3. OPTIMIZATION PHASE

3.1. Conduct of Optimization Phase. If CUSTOMER elects to proceed to the
Optimization Phase and subject to the successful completion of the negotiations
described in Section 2.3, DYAX agrees to devote commercially reasonable
resources and efforts to the diligent conduct of the work to be described in the
Optimization Phase section in the expanded Work Plan Outline of the amended
Exhibit 1. The Optimization Phase is expected to continue for a period to be
determined by such Work Plan Outline and shall end when DYAX has delivered to
CUSTOMER the Optimization Phase Deliverables described in such Work Plan
Outline. During the Optimization Phase, DYAX's Project Director shall meet with
representatives of CUSTOMER at the reasonable request of CUSTOMER to respond to
questions and facilitate the exchange of appropriate information on the progress
of the Optimization Phase. In addition, DYAX shall submit a quarterly summary
progress report to CUSTOMER and, if required by the expanded Work Plan Outline,
a final written report as set forth in the Work Plan Outline.

3.2. Optimization Phase Payments. In consideration of the performance by DYAX of
the Optimization Phase, CUSTOMER agrees to make the payments to DYAX agreed to
by DYAX and CUSTOMER in accordance with Section 2.3 of this Agreement.
*************. In further consideration of the performance by DYAX of the
Optimization Phase, CUSTOMER agrees to pay DYAX a ************* milestone,
payable upon completion of the Optimization Phase if the milestone is achieved.

                       ARTICLE 4. RIGHTS TO DYAX PRODUCTS

4.1 Within ************* of completion of the Development Phase or, if
CUSTOMER elects to proceed with the Optimization Phase, within *************
of completion of the Optimization Phase, CUSTOMER shall notify DYAX of
whether it wishes to acquire an exclusive license to manufacture and use the
Dyax Products for the purification of Customer Product. If CUSTOMER does
desire such a license, then the parties shall promptly meet, negotiate in
good faith and mutually agree upon the terms and conditions of such license
to CUSTOMER, which shall be set forth in a license agreement. Such terms
shall include payment of a license fee, milestone fees and royalties to DYAX,
and shall include an indemnification by DYAX for any claims of patent
infringement brought against CUSTOMER relating to DYAX's technology or
processes, but excluding any claims relating to Customer Product.

                       ARTICLE 5. CONFIDENTIAL INFORMATION
<PAGE>

5.1. Disclosure of Confidential Information.

      (a) In connection with the performance of their respective obligations
under this Agreement, each party intends to disclose certain confidential
information and materials to the other party relating to the Customer Product
and Dyax Products, including such information and materials as are developed
hereunder ( the "Confidential Information"). During the term of this Agreement
and for a period of (5) years thereafter, each party shall maintain all
Confidential Information in strict confidence, except that the Receiving Party
may disclose or permit the disclosure of any Confidential Information to its
directors, officers, employees, consultants, and advisors who are obligated to
maintain the confidential nature of such Confidential Information and who need
to know such Confidential Information for the purposes set forth in this
Agreement; and use all Confidential Information solely for the purposes set
forth in this Agreement.

      (b) The obligations of confidentiality and non-use set forth above shall
not apply to the extent that the Receiving Party can demonstrate that certain
Confidential Information: was in the public domain prior to the time of its
disclosure under this Agreement; entered the public domain after the time of its
disclosure under this Agreement through means other than an unauthorized
disclosure resulting from an act or omission by the Receiving Party; was
independently possessed, developed or discovered by the Receiving Party prior to
the time of its disclosure under this Agreement; or is or was disclosed to the
Receiving Party at any time, whether prior to or after the time of its
disclosure under this Agreement, by a third party having no fiduciary
relationship with the Disclosing Party and having no obligation of
confidentiality with respect to such Confidential Information; or is required to
be disclosed to comply with applicable laws or regulations, or with a court or
administrative order.

                        ARTICLE 6. INTELLECTUAL PROPERTY

6.1. Definitions. As used in this Agreement, the term "Invention" means any
development, conception, technique, process, invention, material, discovery,
or improvement, whether or not patentable, that arises as a result of the
performance of this Agreement. "Dyax Invention" shall mean an Invention,
other than a Customer Invention, that is discovered, developed, conceived, or
reduced to practice during the performance of this Agreement and which
relates to the Dyax Product candidates, including the libraries, affinity
ligands, media and derivatives thereof. "Customer Invention" shall mean an
Invention, other than a Dyax Invention, that is discovered, developed,
conceived, or reduced to practice during the performance of this Agreement
and which relates to CUSTOMER's proprietary technology and/or Customer
Product. Inventions shall be characterized as Dyax Inventions or Customer
Inventions irrespective of whether such Inventions are made by DYAX or
CUSTOMER. In order to effect the foregoing, CUSTOMER agrees to assign to DYAX
any interest it has in any Dyax Invention and DYAX agrees to assign to
CUSTOMER any interest it has in Customer Inventions.

6.2. Ownership & Rights to Intellectual Property. DYAX shall have sole ownership
and control of all Dyax Inventions. CUSTOMER shall have sole ownership and
control of all Customer
<PAGE>

Inventions. Each party's rights to any Invention relevant to the manufacture,
use and sale of a Dyax Product shall be governed by this Agreement and by any
License agreement between the parties.

                         ARTICLE 7. TERM AND TERMINATION

7.1. Term. This Agreement shall commence on the Effective Date and continue
until termination pursuant to this Article 8 or expiration as a result of
CUSTOMER's failure to proceed to continue with this Agreement or as a result of
CUSTOMER's termination pursuant to Section 7.2.

7.2. Termination by CUSTOMER . Provided that CUSTOMER has made all payments
specified in this Agreement which have become due and payable, CUSTOMER shall
have the right to terminate this Agreement at any time by giving 60 days
written notice to DYAX. CUSTOMER agrees to promptly pay DYAX for
uncompensated costs and milestone payments for work completed by DYAX prior
to the termination date, including for any work done during the 60 day
termination notice period. CUSTOMER agrees that no refund of any sums paid to
DYAX shall be due upon any such termination.

7.3. Termination for Material Breach. This Agreement may be terminated by
either party upon 60 days written notice to the other party if any provision
hereof is materially breached, unless such breach is corrected within the 60
- day notice period. Such termination right shall be in addition to, and not
in lieu of, any other rights or remedies available to the non-breaching party
by law or in equity.

7.4. Consequences of Termination and Survival. Upon any termination of this
Agreement by CUSTOMER or by DYAX pursuant to Section 7.3, any rights granted to
CUSTOMER under this Agreement shall cease and DYAX will have the unrestricted
and exclusive right to any Dyax Product, Dyax Inventions and the results of the
Work Plan Outline and CUSTOMER shall have the unrestricted and exclusive right
to any Customer Inventions. Termination of this Agreement shall not relieve
either party of its obligations incurred prior to termination. The provisions of
Article 5. and Article 6 and Section 7.4 shall survive expiration or termination
of this Agreement.

                          ARTICLE 8. GENERAL PROVISIONS

8.1. Notices. Any notices permitted or required by this Agreement shall be sent
by facsimile, registered mail or a recognized private mail carrier service and
shall be effective when received if sent and addressed as follows or to such
other address as may be designated by a party in writing:
<PAGE>

   If to DYAX:                    President, Separations Division
                                  Dyax Corp.
                                  One Kendall Square, Bldg. 600, 5th Fl.
                                  Cambridge, MA  02139
                                  Telephone: (617)225-2500
                                  Fax:       (617)225-2501

   If to CUSTOMER:                Vice President, Process & Product
                                  Development
                                  Genetics Institute, Inc.
                                  One Burtt Road
                                  Andover, MA  01810
                                  Telephone: 508-475-9214
                                  Fax:       508-623-2600

   with a copy to:                Vice President, Law
                                  Genetics Institute, Inc.
                                  87 Cambridge Park Drive
                                  Cambridge, MA  02140
                                  Fax:       617-876-5851

8.2. Entire Agreement; Amendment. This Agreement and the Exhibits set forth the
entire understanding of the parties with respect to the subject matter hereof
and supersedes all prior agreements, written and oral, between the parties. No
modification of any of the terms of this Agreement shall be deemed to be valid
unless it is in writing and signed by the party against whom enforcement is
sought.

8.3. Force Majeure. Neither party shall be held liable or responsible to the
other party nor be deemed to have defaulted under or breached this Agreement for
failure or delay in performing any term of this Agreement when such failure or
delay is caused by or results from causes beyond the reasonable control of the
affected party, including but not limited to fire, floods, embargoes, war, acts
of war (whether war is declared or not), riots, strikes, lockouts or other labor
disturbances, lawsuits, acts of God or acts, omissions or delays in acting by
any court, governmental authority or the other party.

8.4. Warranties. DYAX hereby represents and warrant to CUSTOMER that, to the
best of its knowledge, its use of the technologies and processes contemplated to
be used in performance of this Agreement and the use of the resulting Dyax
Product candidates and Dyax Products will not infringe the intellectual property
rights of any third party; provided, however, that such representation and
warranty shall exclude any intellectual property rights relating to Customer
Product. WITH RESPECT TO ANY DYAX PRODUCT CANDIDATE OR DYAX PRODUCT, DYAX
DISCLAIMS ANY AND ALL WARRANTIES OF ANY KIND, WHETHER EXPRESSED OR IMPLIED,
INCLUDING, BUT NOT LIMITED TO, ANY WARRANTIES OF MERCHANTABILITY OR FITNESS FOR
A PARTICULAR PURPOSE, OR ANY WARRANTIES ARISING FROM COURSE OF DEALING OR USAGE
OF TRADE. Neither
<PAGE>

party shall be liable to the other for consequential, incidental, indirect or
punitive damages arising from the performance or nonperformance of such party
under this Agreement.

8.5. Waiver; Severability. No waiver by either party of any default, right or
remedy shall be effective unless in writing, nor shall any such waiver operate
as a waiver of any other or of the same default, right or remedy, respectively,
on a future occasion. In the event that any term or provision of this Agreement
shall violate any applicable statute, ordinance or rule of law in any
jurisdiction in which it is used, such provision shall be ineffective to the
extent of such violation without invalidating any other provision hereof.

8.6. Assignment. This Agreement may not be assigned or otherwise transferred by
either party without the consent of the other party; provided, however, that
either DYAX or CUSTOMER may, without such consent, assign its rights and
obligations under this Agreement (i) in connection with a corporate
reorganization to an affiliate, all or substantially all of the equity interest
of which is owned and controlled by such party or its parent corporation, or
(ii) in connection with a merger, consolidation or sale of substantially all of
such party's assets to an unrelated third party. Any permitted assignee shall
assume all obligations of its assignor under this Agreement.

8.7. Independent Parties. This Agreement shall not be deemed to create any
partnership, joint venture, or agency relationship between the parties. Each
party hereto is acting as an independent contractor.

8.8. Governing Law. This Agreement shall be governed by and construed under the
laws of the Commonwealth of Massachusetts.

IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first written above.


DYAX CORP.                         GENETICS INSTITUTE, INC.


By: /s/ L. Edward Cannon           By: /s/ Carl R. Illian
    ---------------------------        --------------------------

Name: _________________________    Name: ________________________

Title: ________________________    Title: _______________________


Exhibits
<PAGE>

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

Exhibit 1 - Work Plan Outline
<PAGE>

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

                                WORK PLAN OUTLINE

*************
<PAGE>

March 6, 1998

Dr. Brian Kelley
Principal Engineer
Genetics Institute, Inc.
One Burtt Road
Andover, MA  01810

Re: Development Agreement for Affinity Chromatography Purification Media between
Dyax Corp. and Genetics Institute, Inc. dated September 29, 1997 (the
"Agreement")

Dear Dr. Kelley:

      As we have discussed, we would like to amend the above-referenced
Agreement, as set forth below.

      Section 5.1.(a) of the Agreement shall be amended to add the following
sentence: "The parties also agree that a Receiving Party may disclose the
Confidential Information to existing and prospective commercial partners who are
under like obligations of confidentiality and non-use as set forth in this
Section 5.1, solely for evaluation in connection with purposes set forth in this
Agreement."

      If this agreement accurately sets forth the terms of the amendment, please
sign two copies of this letter and return one to me for our files.


                                    By and on behalf of
                                    DYAX CORP.


                                    By: /s/ Pamela A. Hay
                                        ---------------------------------
                                          Pamela A. Hay
                                          Vice President, Licensing & Legal

AGREED by and on behalf of:
GENETICS INSTITUTE, INC.

/s/ Brian Kelly
----------------------------------

<PAGE>

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

                                   AMENDMENT 1

                                     TO THE

                            DEVELOPMENT AGREEMENT FOR

                   AFFINITY CHROMOTOGRAPHY PURIFICATION MEDIA

      This Amendment (the "Amendment"), effective as of July 20, 1998, is made
by and between DYAX CORP. ("DYAX") and GENETICS INSTITUTE, INC. ("CUSTOMER").

      WHEREAS, DYAX and CUSTOMER are parties to a Development Agreement for
Affinity Chromotography Purification Media of September 29, 1997, as amended by
letter agreement dated March 6, 1998 (the "Agreement"); and

      WHEREAS, the parties wish to amend the Agreement, on the terms and
conditions set forth herein;

      NOW, THEREFORE, the parties hereto agree as follows:

      1. Exhibit 1. The sections entitled ************* and ************* set
forth in Exhibit 1 to the Agreement are hereby deleted in their entirety and
Attachment 1 to this Amendment is hereby substituted in its place as the
revised and complete work plan outline for the *************.

      2. Development Phase. Section 2.2 of the Agreement is hereby deleted in
its entirety and the following language is hereby substituted in its place:

      "(a) In consideration of the performance by DYAX of Part A of the
      Development Phase, CUSTOMER agrees to pay DYAX *************. Such amounts
      shall be payable within 10 days of execution of this Amendment.

      (b) In consideration of the performance by DYAX of Part B of the
      Development Phase, CUSTOMER agrees to pay DYAX *************. Such amounts
      shall be payable *************.

      (c) In further consideration of the work undertaken by DYAX during the
      Development Phase, CUSTOMER agrees to pay DYAX ************* within 30
      days of DYAX's delivery to CUSTOMER ************* which meets the
      milestone requirements for the Development Phase set forth in Part C of
      the Work Plan Outline."

      3. Optimization Phase. Section 3.2 of the Agreement is hereby deleted in
its entirety and the following language is hereby substituted in its place:
<PAGE>

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

      "In consideration of the performance by DYAX of the Optimization Phase,
      DYAX and CUSTOMER shall mutually agree on the amount to be paid by
      CUSTOMER for the Optimization Phase in accordance with Section 2.3.
      One half of such agreed-upon amount shall be paid by CUSTOMER at the
      initiation of the Optimization Phase and one-half of such agreed-upon
      amount shall be paid by CUSTOMER upon the completion of the Optimization
      Phase. In further consideration of the performance by DYAX of the
      Optimization Phase, CUSTOMER shall pay DYAX a milestone fee of
      ************* upon the completion of the Optimization Phase if the
      milestone is achieved. The milestone shall be a process performance
      milestone mutually agreed to by the parties in accordance with
      Section 2.3. The milestone fee ************* shall be creditable against
      the license fee due DYAX in accordance with Section 4.3."

      4. Rights to Dyax Products. Article 4 of the Agreement is hereby deleted
in its entirety and the following language is hereby substituted in its place:

      "4.1. General. Within ************* of completion of the Development
      Phase, or if CUSTOMER elects to proceed with the Optimization Phase,
      within ************* of completion of the Optimization Phase, CUSTOMER
      shall notify DYAX whether it wishes to acquire an exclusive license to
      manufacture and use any or all of the Dyax Products for the purification
      of Customer Product. If CUSTOMER elects to exercise its option to obtain
      such a license, the parties shall promptly meet, negotiate in good faith,
      and mutually agree on the terms and conditions of such license to
      CUSTOMER, which terms and conditions shall be set forth in a license
      agreement. Any such license agreement shall contain the terms and
      conditions set forth in Sections 4.2-4.9 and such other standard terms and
      conditions as are agreed to by the parties. If CUSTOMER does not elect to
      exercise its option to obtain a license to any of the Dyax Products, the
      terms and conditions set forth in Sections 4.2-4.9 shall be of no force
      and effect.

      4.2. License, Right of First Refusal and Exclusive Arrangement.

      (a) DYAX shall grant CUSTOMER an exclusive worldwide license to all
      DYAX know-how and patent rights to make and use the Dyax Products for
      the purpose of purifying (such processes to include, but not be
      limited to, cell culture and transgenic manufacturing) Customer Product
      and/or any other recombinant (but not plasma derived) Factor VIII
      product of CUSTOMER for therapeutic applications (such products so
      purified are hereinafter collectively referred to as "Licensed
      Products"). Such exclusive license shall include the right to
      sublicense to affiliates, third party marketing partners, and contract
      manufacturers. The exclusive license to the DYAX patent rights shall be
      for the life of the DYAX patent rights. The exclusive license to the
      DYAX know-how shall be for a period of 15 years from the first
      commercial sale of the first Licensed Product in any country.
      Thereafter, the know-how license shall convert to a fully-paid up
      non-exclusive license. Subsequent to the expiration of the foregoing
      exclusive licenses (but not pursuant to a conversion to non-exclusivity
      in accordance with Section 4.8), if DYAX grants a non-exclusive license
      to the DYAX know-how to a third party to make and use any of the Dyax
      Products for the purpose of purifying a recombinant Factor VIII product
      for a therapeutic application, CUSTOMER shall be entitled to an
      equitable share (not to exceed 5%) of the licensing revenue received by
      DYAX in respect of such license, such amount to be negotiated by the
      parties in good faith at the time of such license.

<PAGE>

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

      (b) DYAX shall grant CUSTOMER a right of first refusal to expand the
      exclusive licenses to the Dyax Products granted to CUSTOMER for the
      purpose of purifying Licensed Products for therapeutic applications to
      cover the purification of Licensed Products for any *************
      applications of Licensed Products of which either party subsequently
      becomes aware. Each party shall promptly notify the other party of
      any such ************* application of which it becomes aware. CUSTOMER's
      right to exercise the right of first refusal shall be for a period of
      60 days from the date on which DYAX makes a written proposal to CUSTOMER
      for the expansion of the licenses. Alternatively, if DYAX has not made a
      written proposal to CUSTOMER, CUSTOMER may exercise its right of first
      refusal by making a written proposal to DYAX for the expansion of the
      licenses. If CUSTOMER exercises its right of first refusal, the parties
      shall negotiate in good faith the terms of the expansion. In the event
      that (i) CUSTOMER does not exercise its right of first refusal after
      receiving a written proposal from DYAX or (ii) CUSTOMER does exercise its
      right of first refusal and, despite good faith efforts, the parties are
      unable to agree on the terms of any such expansion, DYAX shall have the
      right to license the Dyax Products to a third party for such *************
      application of a recombinant Factor VIII product, provided that the terms
      granted by DYAX to the third party are no more favorable than those last
      offered to CUSTOMER by DYAX.

      (c) In addition to the exclusive licenses to the Dyax Products granted to
      CUSTOMER for therapeutic applications, until the 15th anniversary of the
      first commercial sale of the first Licensed Product in any country or, in
      the event of an earlier conversion to non-exclusivity pursuant to
      Section 4.8, until such conversion, DYAX shall not develop any product on
      behalf of, or license any product to, any other third party for the
      purpose of purifying any form of recombinant Factor VIII product for
      therapeutic applications.

      4.3. License Fee. CUSTOMER shall pay DYAX a license fee ************* upon
      the execution of the license agreement, provided that, in the event that
      CUSTOMER shall have elected to proceed with the Optimization Phase and
      DYAX shall have achieved the process performance milestone agreed upon for
      the Optimization Phase *************.

      4.4 . PRE-LICENSURE EXCLUSIVITY MAINTENANCE FEE. Commencing with the
      first full calendar year subsequent to the calendar year in which CUSTOMER
      enters into the license agreement with Dyax, within 30 days of the
      commencement of each calendar year, CUSTOMER shall pay to DYAX an annual
      exclusivity maintenance fee *************. In any given calendar year,
      CUSTOMER shall be entitled to credit the payment made to DYAX pursuant to
      this Section 4.4 against payments due DYAX in respect of such calendar
      year pursuant to Section 4.5. This provision shall apply until the first
      full calendar year subsequent to the calendar year in which the first
      commercial sale of a Licensed Product occurs. Thereafter, the provisions
      of Section 4.7 shall apply.

      4.5. Benchmark Payments. CUSTOMER shall be required to make the following
      payments to DYAX upon achievement of the following benchmarks,
      *************:

      Benchmark                                       Payment
      ---------                                       -------

      First *************                             *************
      by CUSTOMER or any of its affiliates
      or sublicensees for a Licensed Product

      First *************                             *************
      by CUSTOMER or any of its affiliates or
      sublicensees for a Licensed Product

      First *************                             *************
      by CUSTOMER or any of its affiliates
      or sublicensees for a Licensed Product

      First ************* Licensed                    *************
      Product in the United States or any country
      in Europe by Customer or any of its affiliates
      or sublicensees

      4.6. Royalties. CUSTOMER shall pay DYAX earned royalties at the rate
      ************* of sales of Licensed Products made during each calendar year
      by CUSTOMER and its affiliates and sublicensees and ************* of
      Licensed
<PAGE>

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

      Products ************* made during each calendar year by CUSTOMER and its
      affiliates and sublicensees. With respect to each Licensed Product the
      manufacture of which occurs in a country where the Dyax Product utilized
      in the manufacture is covered by a valid claim of DYAX patent rights,
      royalties shall be payable on such Licensed Product for the life of such
      DYAX patent rights. With respect to each Licensed Product that utilizes a
      Dyax Product in its manufacture, whether or not the manufacture occurs in
      a country where the Dyax Product is covered by a valid claim of DYAX
      patent rights, royalties shall be payable on such Licensed Product for a
      period of 15 years from the first commercial sale of the first Licensed
      Product in any country. Under no circumstances shall CUSTOMER be obligated
      to pay multiple royalties for the licenses to the DYAX patent rights and
      know-how granted pursuant to this Article 4; only one royalty shall be due
      on the sale of a Licensed Product.

      CUSTOMER shall be entitled to deduct 50% of the annual exclusivity
      maintenance fees paid to DYAX pursuant to Section 4.4 and 50% of the
      benchmark payments paid to DYAX pursuant to Section 4.5 from the royalties
      due DYAX pursuant to this Section 4.6; provided that in no calendar year
      shall CUSTOMER be entitled to deduct more than $100,000. Rather, CUSTOMER
      shall be entitled to carry forward from calendar year to calendar year
      amounts not previously deducted due to the foregoing limitation.

      4.7. POST-LICENSURE EXCLUSIVITY MAINTENANCE FEES. Commencing with the
      first full calendar year in which the first commercial sale of a
      Licensed Product occurs, within 30 days of commencement of each
      calendar year, CUSTOMER shall pay DYAX an annual exclusivity
      maintenance fee xxxxxxxxx. In any given calendar year, CUSTOMER shall
      be entitled to credit the payment made to DYAX pursuant to this Section
      4.7 against payments due DYAX in respect of such calendar year pursuant
      to Sections 4.6.

      4.8. Conversion to Non-Exclusivity. In the event that CUSTOMER shall fail
      to pay the annual exclusivity maintenance fee called for by either Section
      4.4 or Section 4.7 in any given calendar year, DYAX's sole remedy shall be
      the right to convert the exclusive licenses granted to CUSTOMER to
      non-exclusive licenses and to convert the exclusive arrangement set forth
      in Section 4.2(c) to a non-exclusive arrangement. **************.

      4.9. Indemnification. The license agreement shall include an
      indemnification by DYAX for any claims of patent infringement brought
      against CUSTOMER relating to DYAX's technology or processes, but
      excluding any claims relating to Licensed Products."

      5. Confidentiality. Section 5.1 of the Agreement is hereby amended to
include an additional sentence at the end thereof as follows:

      "Further, the parties agree that each party may disclose the Confidential
      Information of the other party to Amersham Pharmacia Biotech in order to
      accomplish the purposes of this Agreement, provided that Amersham
      Pharmacia Biotech agrees to obligations of confidentiality and non-use
      which are acceptable to the other party."

      6. Patent Prosecution. Section 6.2 of the Agreement is hereby amended to
include an additional sentence at the end thereof as follows:

      "DYAX agrees to file for patent protection on all Dyax Product candidates
      and such patent rights shall be included in the license grant to CUSTOMER
      pursuant to Article 4."

      7. Capitalization. Capitalized terms used herein and not otherwise defined
shall have the meanings given such terms in the Agreement.

<PAGE>


      8. Other. All other terms and conditions of the Agreement shall remain in
full force and effect.
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have set their hand and seal as of
the date set forth above.

                                          DYAX CORP.

                                          By: ______________________

                                          Name: ____________________

                                          Title: ___________________


                                          GENETICS INSTITUTE, INC.

                                          By: ______________________

                                          Name: ____________________

                                          Title: ___________________

<PAGE>

                            Development Phase Program

*************

<PAGE>

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

                                   AMENDMENT 2
                                     TO THE
                            DEVELOPMENT AGREEMENT FOR
                   AFFINITY CHROMOTOGRAPHY PURIFICATION MEDIA

      This Amendment (the "Amendment"), effective as of March 31, 1999, is made
by and between DYAX CORP. ("DYAX") and GENETICS INSTITUTE, INC. ("CUSTOMER").

      WHEREAS, DYAX and CUSTOMER are parties to a Development Agreement for
Affinity Chromotography Purification Media of September 29, 1997, as amended by
letter agreement dated March 6, 1998 and Amendment 1 dated July 20, 1998 (the
"Agreement"); and

      WHEREAS, the parties wish to further amend the Agreement, on the terms and
conditions set forth herein;

      NOW, THEREFORE, the parties hereto agree as follows:

      1. Optimization Phase. In accordance with Section 2.3 of the Agreement,
CUSTOMER and DYAX acknowledge that CUSTOMER has elected to proceed to the
Optimization Phase. However, notwithstanding the original expectation of the
parties that DYAX would conduct the work to be performed during the Optimization
Phase, CUSTOMER and DYAX agree that CUSTOMER shall conduct the work to be
performed during the Optimization Phase.

      2. Optimization Phase Milestone. In accordance with Section 2.3 of the
Agreement, CUSTOMER and DYAX have agreed to the process performance milestone
for the Optimization Phase set forth in Attachment 1 to this Amendment.

      3. Conduct of Optimization Phase. Section 3.1 of the Agreement is hereby
deleted in its entirety and the following language is substituted in its place:

            "CUSTOMER agrees to devote commercially reasonable and diligent
            efforts to conduct the work necessary to achieve the process
            performance milestone for the Optimization Phase set forth in
            Attachment 1 to this Amendment. During the Optimization Phase,
            CUSTOMER shall provide DYAX's Project Director with regular updates
            on the progress of the Optimization Phase. Upon completion of the
            Optimization Phase, CUSTOMER shall provide DYAX with a final written
            report containing the data and results of the Optimization Phase.
            *************

      4. Optimization Phase Payments. Section 3.2 of the Agreement is hereby
deleted in its entirety and the following language is substituted in its place:

            "CUSTOMER shall be responsible for all costs and expenses associated
            with its performance of the Optimization Phase. In addition,
            CUSTOMER shall pay DYAX a milestone fee ************* upon the
            completion of the Optimization Phase if the process performance
            milestone for the Optimization Phase is achieved by CUSTOMER.
            *************."
<PAGE>

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

      5. Exercise of License. The first sentence of Section 4.1 of the Agreement
is hereby deleted in its entirety and the following language is substituted in
its place:

            "Within ************* of completion of the Optimization Phase, but
            in no event later than *************, CUSTOMER shall notify DYAX
            whether it wishes to acquire an exclusive license to manufacture and
            use any or all of the Dyax Products for the purification of Customer
            Product."

      6. License Fee. Section 4.3 of the Agreement is hereby deleted in its
entirety and the following language is substituted in its place:

            "CUSTOMER shall pay DYAX a license fee ************* upon the
            execution of the license agreement, *************."

      7. Capitalization. Capitalized terms used herein and no otherwise defined
shall have the meanings given such terms in the Agreement.

      8. Other. All other terms and conditions of the Agreement shall remain in
full force and effect.

      IN WITNESS WHEREOF, the parties hereto have set their hand and seal as of
the date set forth above.

                                          DYAX CORP.

                                          By: ______________________
                                          Name: ____________________
                                          Title: ___________________


                                          GENETICS INSTITUTE, INC.

                                          By: ______________________
                                          Name: ____________________
                                          Title: ___________________


<PAGE>

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

                                  Attachment 1

                           Optimization Phase Program

The process performance milestone for the Optimization Phase will be met if all
of the following three criteria are achieved:

*************