SEATTLE--(BUSINESS WIRE)--Oct. 27, 2005--ZymoGenetics, Inc. (Nasdaq:ZGEN) today announced the start of a pivotal Phase 3 clinical study of recombinant human Thrombin (rhThrombin) in patients undergoing surgery. The study will compare the efficacy of rhThrombin to bovine-derived thrombin and is designed to support broad product labeling for the use of rhThrombin as an aid to controlling blood loss during surgery.