Coronary angiography was used to compare the efficacy of anisoylated plasminogen streptokinase activator complex (APSAC) administered intravenously and streptokinase given by intracoronary infusion in inducing reperfusion in patients with a proven acute myocardial infarction. Forty-two patients received 30 U of APSAC intravenously over 5 minutes and 43 patients received 250,000 IU of streptokinase given via intracoronary infusion over 90 minutes, after occlusion of the infarct-related vessel was demonstrated by angiography. Reperfusion was achieved in 23 (64%) of 36 patients (mean time to reperfusion 46 minutes) treated with APSAC and 25 (67%) of 37 patients (mean time to reperfusion 45 minutes) treated with intracoronary streptokinase, who were angiographically evaluated 90 minutes after the start of treatment. Twenty-four hours after treatment, reocclusion had occurred in 1 (5%) of 22 patients in the APSAC group and in 3 (13%) of 23 patients in the streptokinase group. No major bleeding was observed in either treatment group despite a similar systemic lytic state that lasted for up to 48 hours. Two patients treated with APSAC died after severe left ventricular failure unrelated to therapy. The results indicate that APSAC given intravenously is as effective as streptokinase given intracoronary in producing thrombolysis in acute myocardial infarction. The major advantages of APSAC are its rapid and convenient administration by a single intravenous injection, the low rate of arterial reocclusion and good patient tolerance.