Dyax and Genzyme Announce Agreement to Terminate Joint Venture for the Commercialization of DX-88 in HAE.

- Dyax Secures 100% Ownership to DX-88 in All Indications -

-- Conference Call Scheduled for 10 am EST, February 21, 2007 --

CAMBRIDGE, Mass. -- Dyax Corp. (NASDAQ: DYAX) announced today that it has reached a mutual agreement with Genzyme Corporation (NASDAQ: GENZ) to terminate their joint venture for the development and commercialization of DX-88 for hereditary angioedema (HAE). The termination agreement stipulates that Dyax will receive all the assets of the joint venture, including a 100% ownership of DX-88 worldwide, as well as a $17 million cash payment. Genzyme will receive 4.4 million shares of Dyax common stock. Dyax anticipates that this will not affect the Company's 2007 operating activities or the ongoing development and regulatory timelines for DX-88 in HAE.

"This mutual agreement to end our long-standing relationship with Genzyme opens numerous commercialization and partnering opportunities to optimize the value of our DX-88 franchise for both HAE and cardiothoracic surgery (CTS)," stated Henry E. Blair, Chairman and Chief Executive Officer of Dyax. "Our four-year partnership with Genzyme has provided us with the knowledge of orphan indications to move forward from here to complete the development of our HAE program without any delays and reach out to the patient and physician communities to make DX-88 a success in the marketplace."

"The decision to end the HAE joint venture with Dyax is based on a mutual agreement as well as a focus on our rich portfolio of approximately 20 pivotal trials for new products and new indications that will contribute to our future growth," stated Henri A. Termeer, President, Chairman and Chief Executive Officer of Genzyme Corporation. "Our equity interest in Dyax reflects our continued belief in the approvability of DX-88 for HAE, which addresses a tremendous unmet medical need."

About The Joint Venture

Dyax and Genzyme signed the original agreement to jointly develop and commercialize DX-88 for HAE in 1998; Genzyme exercised an option that created the joint venture in 2003. Dyax has been leading the development of DX-88 in HAE, including all clinical, regulatory and manufacturing activities. Through this collaboration, the companies have treated over 200 patients in multiple clinical studies. DX-88's Phase 3, EDEMA3 trial has just recently concluded and Dyax expects to report on the results for the first time in the second quarter of 2007.

About DX-88

DX-88 is a highly specific inhibitor of plasma kallikrein that was discovered and developed by Dyax. Excess plasma kallikrein is thought to play a role in a number of inflammatory and autoimmune diseases. Dyax is developing DX-88 for multiple indications including hereditary angioedema (HAE), a rare genetic disorder and to reduce complications associated with on-pump cardiothoracic surgery (CTS).

DX-88 for HAE is in Phase 3 clinical development and has orphan drug designation in the U.S. and E.U., as well as Fast Track designation in the U.S. for the treatment of acute attacks of HAE. Dyax is just initiating Phase 2 clinical development of DX-88 for CTS.

Webcast and Conference Call

Dyax Corp. will host a webcast and conference call, including an open question and answer session to discuss fourth quarter and year end 2006 financial results and this announcement.

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A replay of the conference call will be available through March 21, 2007 and may be accessed by dialing 888-286-8010. International callers should dial 617-801-6888. The replay passcode for all callers is 25985263. The webcast will be archived on the Dyax website for an indefinite period of time.

About Dyax

Dyax is focused on advancing novel biotherapeutics for unmet medical needs, with an emphasis on oncology and inflammatory indications. Dyax utilizes its proprietary drug discovery technology to identify antibody, small protein and peptide compounds for clinical development.

Dyax's lead product candidate is DX-88, a recombinant small protein that is currently in clinical trials for its therapeutic potential in two separate indications. Dyax has successfully completed three Phase 2 trials and a Phase 3 trial of DX-88 for the treatment of hereditary angioedema (HAE). A confirmatory study, known as EDEMA4, is planned and expected to begin in the first quarter of 2007. DX-88 has orphan drug designation in the U.S. and E.U., as well as Fast Track designation in the U.S. for the treatment of acute attacks of HAE.

Additionally, Dyax has successfully completed a Phase 1/2 trial of DX-88 for the prevention of blood loss during on-pump coronary artery bypass graft (CABG) procedures. Dyax is initiating a Phase 2 trial for further development of DX-88 in on-pump cardiothoracic surgery (CTS), including CABG and heart valve replacement and repair procedures.

Dyax identified DX-88 and other compounds in its pipeline using its patented phage display technology, which rapidly selects compounds that bind with high affinity and specificity to therapeutic targets. Dyax leverages this technology broadly with over 70 revenue generating licenses and collaborations for therapeutic discovery, as well as in non-core areas such as affinity separations, diagnostic imaging, and research reagents.

Dyax is headquartered in Cambridge, Massachusetts, and has antibody discovery facilities in Liege, Belgium. For online information about Dyax Corp., please visit www.dyax.com.

Disclaimer

This press release contains forward-looking statements regarding Dyax Corp., including statements regarding its plans for the clinical development of DX-88 and the effect of the termination of the joint venture with Genzyme on the timelines of the DX-88 program and Dyax's 2007 operating activities. Statements that are not historical facts are based on Dyax's current expectations, beliefs, assumptions, estimates, forecasts and projections for Dyax and the industry and markets in which Dyax competes. The statements contained in this release are not guarantees of future performance and involve certain risks, uncertainties and assumptions, which are difficult to predict. Therefore, actual outcomes and results may differ materially from what is expressed in such forward-looking statements because of uncertainties associated with various activities and aspects of Dyax's business, including risks and uncertainties associated with: the timing and results of clinical trials, regulatory review and approval of Dyax's product candidates, intense competition, including in the areas of DX-88's planned indications, Dyax's efforts to develop and commercialize novel products, its dependence on collaborators for development, clinical trials, manufacturing, sales and distribution of products, Dyax's changing requirements and costs associated with planned research and development activities, the uncertainty of patent and intellectual property protection, Dyax's dependence on key management and key suppliers, the impact of future alliances or transactions involving Dyax or others, and other risk factors described or referred to in Dyax's most recent Annual Report on Form 10-K and other periodic reports filed with the Securities and Exchange Commission. Dyax cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this release, and Dyax undertakes no obligation to update or revise these statements, except as may be required by law.

EDEMA2, EDEMA3, Dyax and the Dyax logo are registered trademarks of Dyax Corp. EDEMA4 is a service mark for Dyax Corp.