Twenty-two patients were infused with 240,000 units streptokinase during a 60-minute period into the ostium of the infarct-related coronary artery (IC), and 23 patients were infused with 1,500,000 units streptokinase intravenously (IV) over 45 minutes; all infusions occurred within 12 hours of the patients' onset of chest pain. Thereafter, heparin was infused for 10 days. Serial coagulation and fibrinolytic parameters were studied over 46 to 72 hours after the streptokinase infusion. A generalized fibrinolytic state was produced in both groups as evidenced by a fall in fibrinogen and plasminogen levels, prolongation of thrombin and reptilase clotting times, a rise in fibrinogen degradation products, and a shortening of the euglobulin lysis time. Recovery to preinfusion levels was similar in both groups of patients. Hemorrhagic complications requiring blood replacement occurred in 7/23 (30%) treated IC, and 4/23 (17%) in the IV group.