News Release

ZymoGenetics to Begin Clinical Study with Interleukin 21; FDA gives go ahead to proceed with Phase 1 cancer study

April 5, 2004

SEATTLE--(BUSINESS WIRE)--April 5, 2004--ZymoGenetics (Nasdaq:ZGEN) announced today that it received agreement from the Food and Drug Administration (FDA) to begin a Phase 1 clinical study with Interleukin 21 (IL-21). IL-21 is a recombinant human protein being developed by ZymoGenetics for the treatment of cancer, initially in metastatic melanoma and renal cell carcinoma. The company expects to open enrollment and begin treating patients in the study within the next several months. The Phase 1 clinical trial will evaluate the safety and pharmacokinetics of recombinant human IL-21.

"New treatments are needed for cancer, and we are very excited about the potential of IL-21 to help cancer patients," said Bruce L. A. Carter, Ph.D., President and Chief Executive Officer of ZymoGenetics. "Metastatic melanoma and metastatic renal cell carcinoma represent significant unmet medical needs. For melanoma, each year there are 56,000 new cases and 8,000 deaths in North America alone. We believe that the ultimate potential of IL-21 could be much larger, presenting opportunities in a number of other cancers."

IL-21 has broad therapeutic potential. There are an estimated 80,000 new cases of melanoma per year worldwide and 100,000 new cases of renal cell carcinoma per year worldwide. Currently, metastatic melanoma and renal cell carcinoma are essentially incurable cancers with no established standard of care. Potential follow-on indications for IL-21 development include other solid tumors, such as lung, colon or breast cancer.

About Interleukin 21 (IL-21)

Interleukin 21 (IL-21) is a novel member of the four helical bundle cytokine family, a protein family which includes several proteins already approved for therapeutic use or in clinical trials. IL-21 was identified using the company's genomics-based discovery platform. IL-21 has potent biological activity in regulating key classes of immune cells, including cytotoxic T cells and natural killer cells. These cell types play key roles in eliminating malignant and infected cells from the body. In preclinical tests, IL-21 stimulated a potent anti-tumor effect and appeared to enhance the ability of cytotoxic T cells to kill cancer cells. Based upon the ability of IL-21 to inhibit tumor growth in a number of animal models and its mechanism of action involving regulation of immune cells, metastatic melanoma and renal cell carcinoma were selected as the initial indications. ZymoGenetics has retained the commercialization rights for IL-21 in North America and has licensed the commercialization rights outside of North America to Novo Nordisk A/S.

About Metastatic Melanoma

The incidence of melanoma is increasing more rapidly than any other cancer in men. In addition, melanoma is the number one cause of cancer in women 25-29 years old. Current therapies are largely ineffective for metastatic melanoma with a median survival of about eight months. Less than five percent of patients diagnosed with metastatic melanoma survive for five or more years. Approved chemotherapy is non-curative.

About Renal Cell Carcinoma

The incidence of renal cell carcinoma is increasing worldwide. In North America, there are 36,000 new cases of renal cell carcinoma each year and 12,000 deaths per year. Current therapies are largely ineffective, with a median survival rate of less than one year. Less than 11 percent of patients diagnosed with renal cell carcinoma survive five years.

About ZymoGenetics

ZymoGenetics is a biopharmaceutical company focused on the discovery, development and commercialization of therapeutic proteins for the prevention or treatment of human diseases. The Company is developing a diverse pipeline of potential proprietary product candidates that are moving into and through clinical development. These 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, 2003. 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.

CONTACT: ZymoGenetics
Susan W. Specht, 206-442-6592

SOURCE: ZymoGenetics