In this study, 30 patients who were to undergo open heart surgery were examined in two separate groups. A high dosage of aprotinin (5 mg/kg) was given before and during cardiopulmonary bypass (CPB) to 20 of the patients. Blood samples were taken from the radial artery at the following times: (1) before anesthesia, (2) 30 minutes into the CPB, (3) at the end of the CPB, (4) 30 minutes after a protamine infusion, (5) 24 hours after surgery. The plasma elastase levels in the aprotonin group were much lower than those in the control group at the 30-minute mark of the CPB (p0.01, for all). Serum fibrinogen levels in the aprotinin group were higher than in the control group at the 30 minute mark of the CPB, at the end of the CPB, and 30 minutes after the protamine infusion (p