<PAGE>


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


                                                                 Exhibit 10.28


                          JOINT COLLABORATION AGREEMENT

THIS LICENSE AGREEMENT (this "Agreement"), effective as of October 1, 1997 (the
"Effective Date"), is between DYAX CORP., a Delaware corporation, having places
of business at One Kendall Square, Bldg. 600, 5th Fl., Cambridge, Massachusetts
02139 and 1500 Avon Street Extended, Charlottesville, VA 22902 ("DYAX"); and
CROPTECH DEVELOPMENT CORPORATION, a Virginia corporation, having its principal
place of business at 1861 Pratt Drive, Blacksburg, Virginia 24060 ("CROPTECH").

                                    RECITALS

WHEREAS, DYAX and CROPTECH have submitted a proposal to the Advanced Technology
Program administered by the National Institute of Standards and Technology
("NIST") to undertake a joint venture to conduct the Researched Program, as
defined herein;

WHEREAS, NIST has selected such proposal for funding, with such funding to be
governed by a NIST Cooperative Agreement;

WHEREAS, DYAX and CROPTECH wish to enter into an agreement setting forth their
respective rights and responsibilities in respect to the Research Program.

WHEREAS, the Parties have selected CropTech Development Corporation to serve as
the Administrator (the "Administrator") for the joint venture and wish to
authorize that organization to perform certain functions, specifically including
execution of the NIST Cooperative Agreement and thereby binding all the Parties
to the terms and conditions of that Agreement.

NOW, THEREFORE, in consideration of the mutual covenants set forth in this
Agreement, the parties hereby agree as follows:

                             ARTICLE 1. DEFINITIONS

For purposes of this Agreement, the terms defined in this Article shall have the
meanings specified below:

1.1. "CropTech Technology" shall mean any and all know-how, data, technology,
equipment, biological or chemical materials, inventions and patent rights
relating to transgenic tobacco and the expression of proteins in transgenic
tobacco plants (including,

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

without limitation the *************), which is owned or controlled by CROPTECH
prior to the Effective Date or which results from the Research Program.

1.2. "Dyax Technology" shall mean any and all know-how, data, technology,
equipment, biological or chemical materials, inventions and patent rights
relating to ************* (including, without limitation, *************), and
which is owned or controlled by DYAX prior to the Effective Date or which
results from the Research Program.

1.3. "Government Use License" shall mean a non-exclusive, non-transferrable,
irrevocable, paid-up license which may be granted to the United States
government as set forth in Section 2.4(d) below.

1.4. "Party" or "Parties" shall mean the parties identified in the Form
NIST-Form-1263 contained in the proposal.

1.5. "Products" shall mean proteins and production technologies utilizing
CropTech Technology and Dyax Technology, and which are listed on Attachment C,
as may be amended from to time by the parties.

1.6. "Research Products" shall mean the research program as described on a
project by project basis in Attachment A, which may be amended from time to time
by the parties.

                           ARTICLE 2. RESEARCH PROGRAM

2.1. Conduct of Research Program. DYAX and CROPTECH agree to work together to
diligently conduct each project of the Research Program, as set forth in
Attachment A hereto, and to carry out their respective responsibilities as set
forth in the Research Program and the NIST Cooperative Agreement. Further, the
parties agree to contribute the funds and internal and external resources which
are set forth in the estimated multi-year budget set forth in Attachment B.

2.2. Administration of the Research Program. The parties agree that CropTech
Development Corporation shall serve as the administrator for the joint
collaboration ("Administrator") and is authorized to execute a NIST Cooperative
Agreement with NIST and communicate with NIST on the progress of each project of
the Research Program. DYAX and CROPTECH shall each promptly appoint two
representatives to a Management Committee. The Management Committee shall meet
no less frequently than semi-annually during Research Program and shall have the
following responsibilities:

      (i)   administering the Research Program in accordance with all legal and
            regulatory requirements, including review of all progress reports;


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

      (ii)  monitor the expenditures of each party for each project in
            accordance with B.

      (iii) discussing and reaching agreement on the ************* of Products
            resulting from each project of the Research Program.

2.3. Record & Reports. Each party shall retain industry standard records of all
data generated during the Research Program. During the Research Program, each
party shall provide the Management Committee, as defined below, with regular
written reports, no less frequently than *************, of the status of the
program and a summary of the data and results as of that date.

2.4. Ownership of Intellectual Property.

      (a)   The protection of intellectual property rights, including any
            invention conceived or first reduced to practice in the course of
            the Research Program, all technical information generated in the
            course of the Research Program and trade secrets under the Research
            Program will be in accordance with the NIST Cooperative Agreement
            and the Proposal which is attached to this Agreement as Attachment D
            subject to Section 2.4(d) below.

      (b)   DYAX shall own all Dyax Technology and CROPTECH shall own all
            CropTech Technology, subject to certain rights retained by the
            government in accordance with the NIST Cooperative Agreement.

      (c)   For inventions resulting from the Research Program, inventorship
            shall be determined in accordance with federal law governing patent
            inventors, and ownership shall be determined in accordance with (a)
            above. Each party shall have responsibility for the cost and
            decisions in filing for, maintaining and defending patent
            applications and patents for their respective inventions. Further
            each party shall provide reasonable cooperation to the other on such
            patent matters.

      (d)   The United States may reserve a nonexclusive, nontransferable,
            irrevocable paid-up license to practice or have practiced for or on
            behalf of the United States any intellectual property that arises
            out of the Research Program, but shall not, in the exercise of such
            license, publicly disclose proprietary information related to such
            license.

      (e)   Dyax and CropTech hereby authorize that, in accordance with the
            Advanced Technology Program rules and regulations, specifically 15
            CFR ss.295.8(a)(1), title to


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            inventions arising from assistance by the Program will vest in a
            company or companies incorporated in the United States. Title to any
            such intellectual property shall not be transferred or passed,
            except to a company incorporated in the United States, until the
            expiration of the first patent obtained in connection with such
            intellectual property. Nothing in this paragraph shall be construed
            to prohibit the licensing to any company of intellectual property
            rights arising from assistance provided under this Section.

2.5. Confidential Information. 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, to include
CropTech Technology and Dyax Technology (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,
advisors and commercial partner candidates 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 each party shall use all Confidential Information solely for the purposes
set forth in this Agreement. The obligations of confidentiality and non-use
set forth above shall not apply to the extent that the receiving party can
demonstrate that Confidential Information: was in the public domain or became
party of the public domain prior through no fault of the receiving party; was
independently developed or discovered by the receiving party prior to the
time of its disclosure under this Agreement; is or was disclosed to the
receiving party at any time by a third party 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 3. COMMERCIAL RIGHTS & OBLIGATIONS

3.1. Commercialization of Products. No later than 90 days of completion of
each project set forth in the Research Program, the parties shall meet and
negotiate and agree upon a joint commercialization plan for the Product
resulting from each project, the terms of which shall be set forth in a
Commercial Agreement. If the parties are unable to reach agreement for any
Product, the matter shall be resolved in accordance with Section 6.2 herein.

3.2. No Rights of License. Except for the rights set forth in this Agreement,
neither DYAX nor CROPTECH grants to the other party any rights or licenses to
any of its trade secrets, know-how, technology, intellectual property or patent
rights.


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<PAGE>

           ARTICLE 4. REPRESENTATIONS AND WARRANTIES & INDEMNIFICATION

4.1. Representations and Warranties. Each party represents and warrants to the
other that it has the legal right and power to enter into this Agreement, to
extend the rights and licenses granted to the other in this Agreement, and to
fully perform its obligations hereunder, and that the performance of such
obligations will not conflict with it charter documents or any agreements,
contracts, or other arrangements to which it is a party. Further, each party
represents and warrants to the other that it will be solely responsible for
analyzing, defending and/or licensing any patent rights of third parties which
relate to its activities for the Research Program.

4.2. Disclaimers. Nothing in this Agreement shall be construed as a warranty or
representation by either party of the success of the Research Program or of the
Dyax Technology or the CropTech Technology.

4.3. Indemnification by DYAX. DYAX agrees to indemnify, defend, and hold
harmless CROPTECH and its directors, officers, employees, and agents (the
"CROPTECH Indemnitees") against any liability, damage, loss or expense
(including reasonable attorneys fees and expenses of litigation) incurred by or
imposed upon any of the CROPTECH Indemnitees as a result of any claims, suits,
actions, demands, or judgments concerning the negligent, willful or infringement
acts of DYAX or its directors, officers, employees, and agents, including,
without limitation, any acts of patent infringement.

4.4. Indemnification by CROPTECH. CROPTECH agrees to indemnify, defend, and hold
harmless DYAX and its directors, officers, employees, and agents (the "DYAX
Indemnities") against any liability, damage, loss or expense (including
reasonable attorneys fees and expenses of litigation) incurred by or imposed
upon any of the DYAX Indemnities as a result of any claims, suits, actions,
demands, or judgments concerning the negligent, willful or infringement acts of
CROPTECH or its directors, officers, employees, and agents, including, without
limitation, any acts of patent infringement.

                        ARTICLE 5. TERM AND TERMINATION.

5.1. Term. Unless sooner terminated as provided herein, this Agreement shall
commence on the Effective Date and shall remain in effect until each
Commercial Agreement is executed, as set forth in Article 3.

5.2. Voluntary Termination. Either party shall have the right to terminate this
Agreement for any reason upon 3 months notice during the Research Program. In
the event of such termination the rights and obligations of the parties shall be
governed by the NIST Cooperative Agreement.


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<PAGE>

5.3. Termination for Material Breach. In the event that either party commits a
material breach of any of its obligations under this Agreement, including
failure to make timely payment of any amounts due, the non-breaching party may
terminate this Agreement upon 60 days written notice to the other party, unless
the party in breach cures such breach within the 60 days notice period.

5.4. Effect of Termination. Notwithstanding anything to the contrary in this
Article 5, upon the expiration of termination of this Agreement, the following
provisions shall survive the expiration or termination of this Agreement:
Articles 4 & 6 and Sections 2.4, and any obligations to NIST or the other party
as set forth in the NIST Cooperative.

                            ARTICLE 6. MISCELLANEOUS

6.1. Notices. All notices required or permitted to be given pursuant to this
Agreement shall be in writing and shall be deemed to have been duly given upon
the date of receipt if delivered by hand, international overnight courier,
confirmed facsimile transmission, or registered or certified mail, return
receipt requested, postage prepaid to the following addresses or facsimile
numbers:

If to DYAX:                             If to CROPTECH:
Dyax Corp.                              CropTech Development Corporation
One Kendall Square                      1861 Pratt Drive
Bldg. 600 5th Fl.                       Blacksburg, VA 24060
Cambridge, MA 02139                     Attention: Chief Executive
Attention: Chief Executive Officer      Officer
Facsimile: (617) 225-2501               Facsimile: (540) 231-8223

Either party may change its designated address and facsimile number by notice to
the other party in the manner provided in this Section.

6.2. Dispute Resolution. In the event either party has a dispute regarding
any of the terms of this Agreement, that party shall notify the other party
in writing. The parties shall use their best efforts to resolve the dispute
amicably at the Management Committee, or if the Management Committee is
unsuccessful in reaching resolution, the parties shall refer the matter for
resolution by their Chief Executive Officers. If such attempts are not
successful in resolving the dispute within a period of 60 days following the
notice of dispute, either party may refer the dispute to the American
Arbitration Association for hearing and resolution within 6 months, using one
mutually agreed upon arbitrator with industry experience relevant to this
Agreement and at a forum in the Charlottesville, Virginia area. Upon
reference of the dispute for arbitration, neither party shall contest such
dispute in a court of law until the completion of the arbitration process.

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6.3. Powers of Attorney. By signing this Agreement, the Parties grant to
Administrator a Power of Attorney for the sole purpose of binding each Party to
the terms and conditions of the NIST Cooperative Agreement.

6.4. Press Releases & Use of Names. The parties shall mutually agree upon any
press release or similar public disclosure concerning this Agreement.

6.5. Headings & Counterparts. All headings in this Agreement are for convenience
only and shall not affect the meaning of any provisions hereof. This Agreement
may be executed in one or more counterparts, each of which shall be deemed an
original, and all of which together shall be deemed to be one and the same
instrument.

6.6. Assignment. This Agreement may not be assigned by either party without the
prior written consent of the other party, except that either party may assign
this Agreement to any of its Affiliates or to a successor in connection with the
merger, consolidation, or sale of all or substantially all of its assets or that
portion of its business pertaining to the subject matter of this Agreement, with
prompt written notice to the other party of any such assignment.

6.7. Compliance With Law. Nothing in this Agreement shall be construed so as to
require the commission of any act contrary to law, and wherever there is any
conflict between any provision of this Agreement and any statute, law, ordinance
or treaty, the latter shall prevail, but in such event the affected provisions
of the Agreement shall be conformed and limited only to the extent necessary to
bring it within the applicable legal requirements.

6.8. Amendment and Waiver. This Agreement may be amended, supplemented, or
otherwise modified only by means of a written instrument signed by both parties.
Any waiver of any rights or failure to act in specific instance shall relate
only to such instance and shall not be construed as an agreement to waive any
rights or fail to act in any other instance, whether or not similar.

6.9. Precedence. Should there be any conflict between the terms and conditions
of this Agreement and the NIST Cooperative Agreement, the NIST Cooperative
Agreement shall take precedence.

6.10. Severability. In the event that any provision of this Agreement shall, for
any reason, be held to be invalid or unenforceable in any respect, such
invalidity or unenforceability shall not affect any other provision hereof, and
the parties


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

shall negotiate in good faith to modify the Agreement to preserve their original
intent.

6.11. Entire Agreement. This Agreement constitutes the entire agreement between
the parties with respect to the subject matter hereof and supersedes all prior
agreements or understandings between the parties relating to the subject matter
hereof.

IN WITNESS WHEREOF, the undersigned have duly executed and delivered this
Agreement as a sealed instrument effective as of the date first above written.


DYAX CORP.                         CROPTECH DEVELOPMENT CORPORATION


By: /s/ Henry E. Blair             By: /s/ David N. Radin
Name: Henry E. Blair               Name: David N. Radin
Title: Chairman & CEO              Title: President


Attachments:

Attachment A: *************
Attachment B: *************
Attachment C: *************
Attachment D: *************


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

                                  Attachment A

                      Research Program (project by project)

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


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

                                  Attachment B
                                Multi-year Budget

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


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

                                  Attachment C
                                    Products

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


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

                                  Attachment D
                                  NIST Proposal

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


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