Dyax Initiates Confirmatory Phase 3 (EDEMA4) Trial for DX-88 for the Treatment of Hereditary Angioedema.

CAMBRIDGE, Mass. -- Dyax Corp. (Nasdaq:DYAX) announced today that patient treatment has begun in the Phase 3 confirmatory trial, known as EDEMA4, for its lead product candidate, DX-88 (ecallantide). DX-88, an internally discovered, recombinant, plasma kallikrein inhibitor, is in clinical trials for the treatment of acute attacks of hereditary angioedema (HAE), a rare genetic disease characterized by episodes of acute swelling and inflammation. Dyax is also initiating a Phase 2 clinical trial of DX-88 for the prevention of blood loss that occurs during on-pump cardiothoracic surgery.

EDEMA4 will be used to further support the validity of the patient reported outcome (PRO) methodology used in the successfully completed Phase 3 trial, EDEMA3, and to confirm efficacy and safety. The trial will take place at approximately 40 sites in the United States and will include patients previously exposed to DX-88 as well as naove patients. The trial will be conducted as a double-blind, placebo-controlled study where patients will receive a single 30 mg subcutaneous dose of DX-88 or placebo. Patients completing the trial will be allowed continued access to DX-88 through an open-label continuation study. The trial is being conducted under a Special Protocol Assessment (SPA) agreed upon with the U.S. Food and Drug Administration (FDA).

"We are extremely excited about treating the first patient in the EDEMA4 trial," remarked Dr. Stacie Jones, Principal Investigator from Arkansas Children's Hospital. "Currently, there is no treatment for HAE in the United States. With the start of this trial, Dyax is one step closer to potentially having a drug being approved and on the market for the HAE patient community. We are enthusiastic about our participation in the EDEMA4 trial and look forward to its rapid conclusion."

"We are excited to be approaching the final stages of our HAE program. Based on the rapid completion and positive topline results of EDEMA3 and our close relationship with the HAE community, we believe we will be able to quickly enroll patients for this trial," commented Henry E. Blair, Chairman and Chief Executive Officer of Dyax. "Dyax remains steadfast in its commitment to deliver to the marketplace this treatment and anticipates receiving approval in late 2008."

DX-88 for HAE Program Summary

Dyax has completed three Phase 2 trials, referred to as EDEMA0, EDEMA1, and EDEMA2, and a Phase 3 trial, EDEMA3, to evaluate DX-88 for the treatment of acute attacks of HAE. Dyax continues to build upon the extensive clinical data accumulated through the DX-88 HAE program. As of early April, over 250 individuals have been treated with more than 660 doses of DX-88.

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, has begun in April 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.

Dyax Disclaimer

This press release contains forward-looking statements, including statements regarding the clinical trials and plans for the development of DX-88 for HAE and CTS. Statements that are not historical facts are based on Dyax's current expectations, beliefs, assumptions, estimates, forecasts and projections about 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. Important factors which may affect the clinical trials and plans for the development of DX-88 for HAE and CTS include the risks that: DX-88 may not show sufficient therapeutic effect or an acceptable safety profile in clinical trials or could take a significantly longer time to gain regulatory approval than Dyax expects or may never gain approval in HAE or CTS; others may develop technologies or products superior to DX-88 in HAE or CTS or that are on the market before DX-88; DX-88 may not gain market acceptance in HAE or CTS; Dyax is dependent on the expertise, effort, priorities and contractual obligations of third parties in the clinical trials and manufacture of DX-88 and Dyax is subject to 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 obligations to update or revise these statements, except as may be required by law.

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