Bleeding can be a serious complication of surgery, and topical thrombin is widely used as an adjunct to hemostasis in diverse surgical settings. The potent hemostatic properties of thrombin derive from its ability to activate platelets directly to aggregate and adhere to damaged vessels and to catalyze the formation simultaneously of a fibrin matrix. Application of exogenous thrombin bypasses the physiological process of generating a thrombin burst by directly initiating the terminal reactions of blood clot formation. Currently, thrombin used to control surgical bleeding is primarily from bovine plasma, with a small percentage from human plasma. Human thrombin isolated from pooled plasma carries the risk of transmitting plasma-borne pathogens or prion diseases. The bovine preparations have been associated with protein and preparative contaminants that pose potential risks of developing cross-reacting antibodies. There is a need for a pure therapeutic preparation of human thrombin. Recombinant human thrombin (rhThrombin) has been efficiently produced from a prethrombin-1 precursor obtained from Chinese hamster ovary cell culture. This rhThrombin is substantially free of process-derived contaminants and has been characterized extensively in terms of composition, primary, secondary, and tertiary structure, enzymatic activity; and in vivo pharmacology. In vivo studies of topically applied rhThrombin have shown it is effective in achieving hemostasis in a rabbit liver excisional wound model. Clinical studies are ongoing to evaluate the safety and efficacy of rhThrombin as an adjunct to hemostasis in patients undergoing surgery.