<PAGE>

                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                                   FORM 10-K/A

/X/ Amendment No. 1 to Annual Report Pursuant to Section 13 or 15(d) of the
Securities Exchange Act of 1934

For the fiscal year ended December 31, 2001 OR

/ / Transition Report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934 for the transition period from __________ to
     __________

                        Commission File Number 000-24537

                                   DYAX CORP.
               --------------------------------------------------
               (EXACT NAME OF COMPANY AS SPECIFIED IN ITS CHARTER)

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       Delaware                                         04-3053198
------------------------                      ---------------------------------
(STATE OF INCORPORATION)                      (IRS EMPLOYER IDENTIFICATION NO.)
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              300 Technology Square, Cambridge, Massachusetts 02139
           -----------------------------------------------------------
              (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES AND ZIP CODE)

         Company's telephone number, including area code: (617) 250-5500
                                                          --------------

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Securities registered pursuant to Section 12(b) of the Act:   NONE
                                                              ----

Securities registered pursuant to Section 12(g) of the Act:   COMMON STOCK, $.01 PAR VALUE
                                                              ----------------------------
                                                              (TITLE OF CLASS)
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Indicate by checkmark whether the Company (1) has filed all reports required to
be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the Company was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days. YES /X/   NO

Indicate by checkmark if disclosure of delinquent filers pursuant to Item 405 of
Regulation S-K is not contained herein, and will not be contained, to the best
of Company's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. / /

The aggregate market value of the Company's common stock, par value $.01 per
share, held by nonaffiliates of the Company as of March 25, 2002, based on the
last reported sale price of the Company's common stock on The Nasdaq National
Market as of the close of business on that day, was $64,381,724. The number of
shares outstanding of the Company's common stock as of March 25, 2002, was
19,579,489.

                       DOCUMENTS INCORPORATED BY REFERENCE

Portions of the Company's Definitive Proxy Statement for its 2002 Annual Meeting
of Stockholders to be held on May 16, 2002, which Definitive Proxy Statement was
filed with the Securities and Exchange Commission on April 22, 2002, are
incorporated by reference into Part III of the Company's Form 10-K for the
fiscal year ended December 31, 2001.

EXPLANATORY NOTE:

Dyax Corp. hereby amends its Annual Report on Form 10-K for the year ended
December 31, 2001, as filed with the Securities and Exchange Commission on April
1, 2002, for the purposes of (i) filing as Exhibit 3.4 a Certificate of
Correction to the Restated Certificate of Incorporation which corrects certain
typographical errors therein, (ii) re-filing as Exhibit 10.1 the correct form of
its current Amended and Restated 1995 Equity Incentive Plan previously approved
by stockholders, and (iii) filing an updated Exhibit 21.1, Subsidiaries of the
Registrant. There have been no changes to the financial data.

Pursuant to Rule 12b-15 under the Securities Exchange Act of 1934, this
amendment contains the complete text of Item 14, the item being amended. The
Index to Exhibits, which is incorporated by reference into Item 14, indicates
the exhibits being filed herewith.

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                                     PART IV

ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K

(A.) 1. FINANCIAL STATEMENTS

The financial statements are included under Part II, Item 8 of the Company's
Annual Report on Form 10-K for the fiscal year ended December 31, 2001.

2. FINANCIAL STATEMENT SCHEDULE

                 SCHEDULE II--VALUATION AND QUALIFYING ACCOUNTS
                FOR THE YEARS ENDED DECEMBER 2001, 2000, AND 1999
                                 (IN THOUSANDS)

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                                               BALANCE AT
                                              BEGINNING OF                                   BALANCE AT END
                                                    PERIOD       ADDITIONS      DEDUCTIONS        OF PERIOD
                                              ------------       ---------      ----------   --------------
<S>                                           <C>                <C>            <C>          <C>
Allowance for Doubtful Accounts:
  2001...............................                 $130             $25              --             $155
  2000...............................                 $129              $1              --             $130
  1999...............................                 $129              --              --             $129
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<CAPTION>
                                                BALANCE AT
                                              BEGINNING OF                                   BALANCE AT END
                                                    PERIOD       ADDITIONS      DEDUCTIONS        OF PERIOD
                                              ------------       ---------      ----------   --------------
<S>                                           <C>                <C>            <C>          <C>
Deferred Tax Asset Valuation
Allowance:
  2001...............................              $27,596          $5,926              --          $33,522
  2000...............................              $21,916          $5,680              --          $27,596
  1999...............................              $16,541          $5,375              --          $21,916
</TABLE>

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                                                BALANCE AT
                                              BEGINNING OF                                   BALANCE AT END
                                                    PERIOD       ADDITIONS      DEDUCTIONS        OF PERIOD
                                              ------------       ---------      ----------   --------------
<S>                                           <C>                <C>            <C>          <C>
Accrued warranty costs:
  2001...............................                 $146            $150              --             $296
  2000...............................                 $146              --              --             $146
  1999...............................                 $160              --           $(14)             $146
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3. EXHIBITS

The exhibits are listed below under Part IV, Item 14(c) of this Report.

(B.) REPORTS ON FORM 8-K

We did not file any Current Reports on Form 8-K during the quarter ended
December 31, 2001.

<PAGE>

(C.) EXHIBITS

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<CAPTION>
EXHIBIT NO.     DESCRIPTION
<S>             <C>

3.1             Restated Certificate of Incorporation of the Company. Filed as
                Exhibit 3.1 to the Company's Quarterly Report on Form 10-Q (File
                No. 000-24537) for the quarter ended September 30, 2000 and
                incorporated herein by reference.

3.2             Amended and Restated By-laws of the Company. Filed as Exhibit
                3.2 to the Company's Quarterly Report on Form 10-Q (File No.
                000-24537) for the quarter ended September 30, 2000 and
                incorporated herein by reference.

3.3             Certificate of Designations Designating the Series A Junior
                Participating Preferred Stock of the Company. Filed as Exhibit
                3.1 to the Company's Current Report on Form 8-K (File No.
                000-24537) and incorporated herein by reference.

3.4             Certificate of Correction to the Restated Certificate of
                Incorporation of the Company. Filed herewith.

4.1             Specimen Common Stock Certificate. Filed as Exhibit 4.1 to the
                Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

4.2             Rights Agreement, dated June 27, 2001 between American Stock
                Transfer & Trust Company, as Rights Agent, and the Company.
                Filed as Exhibit 4.1 to the Company's Current Report on Form 8-K
                (File No. 000-24537) and incorporated herein by reference.

10.1            Amended and Restated 1995 Equity Incentive Plan, as amended
                through October 2001. Filed herewith.

10.2            1998 Employee Stock Purchase Plan. Filed as Exhibit 10.2 to the
                Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

10.3            The 1995 Amended and Restated Equity Incentive Plan Inland
                Revenue Approved Sub-Plan for the United Kingdom, as amended on
                October 26, 2001. Previously filed.

10.4*           Employment Letter Agreement, dated September 1, 1999, between
                Stephen S. Galliker and the Company. Filed as Exhibit 10.3 to
                the Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

10.5*           Restricted Stock Purchase Agreement, dated October 1999, between
                Stephen S. Galliker and the Company. Filed as Exhibit 10.4 to
                the Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

10.6*           Restricted Stock Purchase Agreement, dated November 30, 1999,
                between Stephen S. Galliker and the Company. Filed as Exhibit
                10.5 to the Company's Registration Statement on Form S-1 (File
                No. 333-37394) and incorporated herein by reference.

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10.7*           Letter Agreement, dated as of September 1, 1998, between Gregory
                D. Phelps and the Company. Filed as Exhibit 10.6 to the
                Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

10.8*           Letter Agreement dated May 21, 1999 between Scott Chappel and
                the Company. Filed as Exhibit 10.7 to the Company's Annual
                Report on Form 10-K for the year ended December 31, 2000 (File
                No. 000-24537) and incorporated herein by reference.

10.9*           Consulting Agreement, dated October 15, 1997, between James W.
                Fordyce and the Company. Filed as Exhibit 10.9 to the Company's
                Registration Statement on Form S-1 (File No. 333-37394) and
                incorporated herein by reference.

10.10*          Loan and Pledge Agreement, dated October 30, 1998, between Henry
                E. Blair and the Company. Filed as Exhibit 10.10 to the
                Company's Annual Report on Form 10-K for the year ended December
                31, 2000 (File No. 000-24537) and incorporated herein by
                reference.

10.11*          Loan Agreement dated June 14, 1999 between Scott Chappel and the
                Company. Filed as Exhibit 10.11 to the Company's Annual Report
                on Form 10-K for the year ended December 31, 2000 (File No.
                000-24537) and incorporated herein by reference.

10.12           Lease, dated June 30, 1999, between Alan G. Dillard, Jr., and
                the Company. Filed as Exhibit 10.13 to the Company's
                Registration Statement on Form S-1 (File No. 333-37394) and
                incorporated herein by reference.

10.13           Lease Agreement, dated as of February 12, 1998, between AStec
                Partnership and the Company. Filed as Exhibit 10.14 to the
                Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

10.14           Lease Agreement, dated as of February 11, 1997, between AStec
                Partnership and the Company. Filed as Exhibit 10.15 to the
                Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

10.15           Lease Agreement, dated April 8, 1991, between Bridge Gate Real
                Estates Limited, Harforde Court Management Limited and the
                Company. Filed as Exhibit 10.18 to the Company's Registration
                Statement on Form S-1 (File No. 333-37394) and incorporated
                herein by reference.

10.16           Master Lease Agreement, dated December 30, 1997, between
                Transamerica Business Credit Corporation and the Company. Filed
                as Exhibit 10.21 to the Company's Registration Statement on Form
                S-1 (File No. 333-37394) and incorporated herein by reference.


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10.17           Form of Sale and Leaseback Agreement, dated December 30, 1997,
                between Transamerica Business Credit Corporation and the
                Company. Filed as Exhibit 10.22 to the Company's Registration
                Statement on Form S-1 (File No. 333-37394) and incorporated
                herein by reference.

<S>             <C>
10.18           Form of License Agreement (Therapeutic Field) between the
                Licensee and the Company. Filed as Exhibit 10.23 to the
                Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

10.19           Form of License Agreement (Antibody Diagnostic Field) between
                the Licensee and the Company. Filed as Exhibit 10.24 to the
                Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

10.20           Collaboration Agreement between Genzyme Corporation and the
                Company, dated October 1, 1998. Filed as Exhibit 10.25 to the
                Company's Registration Statement on Form S-1 (File No.
                333-37394) and incorporated herein by reference.

10.21+          License Agreement, dated January 24, 2001, between Debiopharm
                S.A. and the Company. Filed as Exhibit 10.26 to the Company's
                Annual Report on Form 10-K for the year ended December 31, 2000
                (File No. 000-24537) and incorporated herein by reference.

10.22+          License, Technology Transfer, and Technology Services Agreement,
                dated February 2, 2000, between Amgen Inc. and the Company.
                Filed as Exhibit 10.30 to the Company's Registration Statement
                on Form S-1 (File No. 333-37394) and incorporated herein by
                reference.

10.23+          Collaboration and License Agreement, dated March 17, 2000,
                between Human Genome Sciences, Inc. and the Company. Filed as
                Exhibit 10.31 to the Company's Registration Statement on Form
                S-1 (File No. 333-37394) and incorporated herein by reference.

10.24           Amendment to the Collaboration and License Agreement, dated July
                1, 2001, between Human Genome Sciences, Inc. and the Company.
                Filed as Exhibit 10.1 to the Company's Quarterly Report on Form
                10-Q for the quarter ending September 30, 2001 (File No.
                000-24537) and incorporated herein by reference.

10.25           Form of Indemnification Agreement by and between certain
                directors and executive officers of the Company and the Company.
                Filed as Exhibit 10.32 to the Company's Registration Statement
                on Form S-1 (File No. 333-37394) and incorporated herein by
                reference.

10.26           Amended and Restated Registration Rights Agreement, dated as of
                February 12, 2001, between holders of the Company's capital
                stock named therein and the Company. Filed as Exhibit 10.33 to
                the Company's Annual Report on Form 10-K for the year ended
                December 31, 2000 (File No. 000-24537) and incorporated herein
                by reference.

10.27           Master Loan and Security Agreement, dated June 30, 2000, between
                Transamerica Business Credit Corporation and the Company. Filed
                as Exhibit 10.35 to the Company's Registration Statement on Form
                S-1 (File No. 333-37394) and incorporated herein by reference.

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10.28+          Collaboration and License Agreement, dated October 31, 2000,
                between Bracco Holding, B.V. and Bracco International, B.V. and
                the Company. Filed as Exhibit 10.2 to the Company's Quarterly
                Report on Form 10-Q (File No. 000-24537) for the quarter ended
                September 30, 2000 and incorporated herein by reference.

10.29           Lease, dated June 13, 2001, between the Massachusetts Institute
                of Technology and the Company. Filed as Exhibit 10.1 to the
                Company's Quarterly Report on Form 10-Q (File No. 000-24537) for
                the quarter ended June 30, 2001 and incorporated herein by
                reference.

21.1            Subsidiaries of the Company. Filed herewith.

23.1            Consent of PricewaterhouseCoopers LLP, independent accountants.
                Previously filed.

99.1            Factors Affecting Future Operations and Results. Previously
                filed.
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*Indicates a contract with management.

+This Exhibit has been filed separately with the Commission pursuant to an
application for confidential treatment. The confidential portions of this
Exhibit have been omitted and are marked by an asterisk.

<PAGE>

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the Company has duly caused this report to be signed on its behalf
by the undersigned, thereunto duly authorized, this 23rd day of April, 2002.

                                          DYAX CORP.

                                          /s/ Stephen S. Galliker
                                          -------------------------------------
                                          Stephen S. Galliker
                                          Executive Vice President, Finance and
                                          Administration, Chief Financial
                                          Officer and Treasurer