The ability of anisoylated plasminogen: streptokinase activator complex (APSAC) to induce coronary artery reperfusion after bolus intravenous injection (2 to 4 minutes) was assessed in 29 patients with acute transmural myocardial infarction and complete coronary artery occlusion. A 5-mg dose resulted in reperfusion in 3 of 14 patients (21%); a 5-mg plus 10-mg regimen was successful in 3 of 7 (43%); and a 30-mg dose induced reperfusion in 9 of 15 (60%). Rethrombosis occurred in only 1 of 15 patients (7%) who received 30 mg, as determined by repeat angiography at 24 hours. The mean interval after injection until reperfusion was 35 minutes with the 30-mg dose, and bleeding occurred at the femoral artery catheterization site in only 3 of 15 patients (20%). Intracoronary streptokinase therapy achieved reperfusion in only 2 of the 6 patients in whom the 30-mg dose failed, indicating that this dose of APSAC was sufficient by itself in 9 of 11 (83%) successfully treated patients. Because therapy can be completed within 2 to 4 minutes, APSAC appears to be a most suitable fibrinolytic agent for early treatment of the coronary artery thrombosis associated with acute transmural myocardial infarction.