ZymoGenetics, Inc. Completes Enrollment For rhThrombin Phase 3 Trial

SEATTLE, June 20 /PRNewswire-FirstCall/ -- ZymoGenetics, Inc. today announced it has completed patient enrollment for a Phase 3 pivotal clinical trial of recombinant human thrombin (rhThrombin) as an aid to controlling blood loss during surgery. The Phase 3 trial data will be analyzed in the third quarter and the company plans to disclose outcomes and present the study results at a scientific meeting before year end.

The pivotal Phase 3 clinical trial was designed to compare rhThrombin to bovine thrombin (the currently marketed product) in four surgical settings and to evaluate the safety, efficacy and immunogenicity of the two products. The study was designed to enroll 400 - 600 patients and, based on the recommendation of an independent data monitoring committee following a planned interim analysis, 400 evaluable subjects provided sufficient power for the planned efficacy comparison. Assuming the endpoints in the study are met, ZymoGenetics plans to submit a Biologics Licensing Application (BLA) for rhThrombin to the FDA in late 2006.

“Through the motivation of our external clinical investigators and hard work of our internal staff, we were able to complete patient enrollment on schedule,” said Nicole Onetto, M.D., Senior Vice President and Chief Medical Officer of ZymoGenetics. “This allows us to continue to pursue our plan for submission of a BLA to the FDA by year end and, we hope, to provide an effective and safe alternative for the control of surgical bleeding.”

About rhThrombin

ZymoGenetics is developing rhThrombin for the control of bleeding associated with surgical procedures. Thrombin is used in more than 700,000 surgeries each year in the United States. Currently, only thrombin derived from bovine blood is available in the U.S. as a stand-alone thrombin product. Bovine-derived thrombin has been associated with the development of antibodies that may cross-react with human blood proteins and in some cases these antibodies appear to be related to serious bleeding complications. The production of recombinant proteins is not dependent on the availability of blood from human or animal donors and can be scaled-up to meet market demands.

About ZymoGenetics

ZymoGenetics creates novel protein drugs with the potential to significantly help patients fight their diseases. The Company is developing a diverse pipeline of potential proprietary product candidates that are moving into and through clinical development. These candidates span a wide array of clinical opportunities that include bleeding, autoimmune diseases and cancer. ZymoGenetics intends to commercialize these product candidates through internal development, collaborations with partners, and out-licensing of patents from its extensive patent portfolio. For further information, visit www.zymogenetics.com.

This press release contains “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements are based on the current intent and expectations of the management of ZymoGenetics. These statements are not guarantees of future performance and involve risks and uncertainties that are difficult to predict. ZymoGenetics’ actual results and the timing and outcome of events may differ materially from those expressed in or implied by the forward-looking statements because of risks associated with our unproven discovery strategy, preclinical and clinical development, regulatory oversight, intellectual property claims and litigation and other risks detailed in the company’s public filings with the Securities and Exchange Commission, including the company’s Annual Report on Form 10-K for the year ended December 31, 2005. Except as required by law, ZymoGenetics undertakes no obligation to update any forward-looking or other statements in this press release, whether as a result of new information, future events or otherwise.

Investor Relations John Calhoun, MD, MBA Director, Corporate Communications & Investor Relations 206-442-6744 Media Relations Susan W. Specht, MBA Associate Director, Corporate Communications 206-442-6592

ZymoGenetics

CONTACT: investors, John Calhoun, MD, MBA, Director, CorporateCommunications & Investor Relations, +1-206-442-6744, or media, Susan W.Specht, MBA, Associate Director, Corporate Communications, +1-206-442-6592,both of ZymoGenetics

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