The effects of Argatroban, a selective thrombin inhibitor, in anticoagulation therapy following cardiovascular surgery is reported. The agent was administered in 28 patients by means of continuous intravenous infusion, adjusted to maintain the activated coagulation time at from 170 to 200 seconds. The activated coagulation time was well controlled at a mean rate of 0.482± 0.26μg/kg/min by intravenous drip infusion, and the dose of Argatroban reached a steady state within a few hours. Both the percent rate of prothrombin time and the activated partial thromboplastin time were significantly decreased to 49% and to 36% respectively by Argatroban, and recoverd to the normal range the day after cessation of the drug. Thrombin-antithrombin III complex, an index of coagulation activity, decreased from 35μg/l in the postoperative state to 14 μg/l 4 hours after the infusion of the drug, which demonstrated the good control of anticoagulation status. Clinically, no adverse reactions such as abnormal bleeding tendency was observed. We conclude that Argatroban is a safe and effective agent for anticoagulation therapy in the early postoperative phase.