News Release

FDA Grants Orphan Drug Designation to ZymoGenetics' IL-21 for Treatment of Melanoma

October 5, 2005

SEATTLE--(BUSINESS WIRE)--Oct. 5, 2005--ZymoGenetics, Inc. (Nasdaq:ZGEN) today announced that the U.S. Food and Drug Administration (FDA) has granted Orphan Drug designation to Interleukin 21 (IL-21) for the treatment of melanoma patients with advanced or aggressive disease. ZymoGenetics is testing IL-21 in an ongoing Phase 1b clinical trial in melanoma and renal cell carcinoma with a dosing regimen administered in an outpatient setting.

"We're excited about the progress of the IL-21 program," said Dr. Bruce L.A. Carter, President and CEO of ZymoGenetics. "Our studies have shown that IL-21 stimulates cells of the immune system that are thought to have a critical role in eliminating malignant cells. We believe IL-21 may come to play an important role in helping cancer patients who need an effective therapy with manageable side effects."

About the FDA Orphan Drug Designation

The FDA Orphan Drug designation is reserved for promising new therapies being developed to treat diseases that affect fewer than 200,000 people in the United States. The Orphan Drug Act guarantees market exclusivity for seven years to the first sponsor that obtains market approval for an orphan-designated product. This designation provides companies with financial and regulatory benefits during the course of orphan drug development, including tax credits related to clinical trial expenses.

About Melanoma

Melanoma is a form of skin cancer that spreads rapidly if not caught at an early stage. The American Cancer Society estimates that this year, nearly 60,000 Americans will be diagnosed with melanoma, and almost 8,000 patients will die from the disease. Nearly a quarter of melanoma patients have advanced or aggressive (Stages IIB-T4a and beyond) forms of the disease, and only thirty-nine percent of those patients are currently projected to survive beyond five years from the time of diagnosis. (Balch, C., et al; Final version of the American Joint Committee on Cancer Staging System for Cutaneous Melanoma. Journal of Clinical Oncology, Vol. 19, No. 16 (August 15), 2001: pp 3635-3648)

About Interleukin 21 (IL-21)

IL-21 is a novel cytokine with potent effects on a number of immune effector cells such as cytotoxic T cells and natural killer cells. These cell types are thought to play key roles in eliminating malignant and infected cells from the body.

Metastatic melanoma and renal cell carcinoma, two tumors which have been shown to be responsive to immune based therapies, were selected as the initial indications. In addition, IL-21 has been shown to inhibit tumor growth in animal models of melanoma and renal cell carcinoma with a mechanism involving regulation of immune cells. ZymoGenetics has retained the commercialization rights for IL-21 in North America and licensed the commercialization rights outside of North America to Novo Nordisk A/S.

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, 2004. 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, Inc.
Investor Relations
John Calhoun, MD, MBA
Director, Corporate Communications & Investor Relations
206-442-6744
or
Media Relations
Susan W. Specht, MBA
Corporate Communications Manager
206-442-6592

SOURCE: ZymoGenetics, Inc.