Anisoylated plasminogen streptokinase activator complex (APSAC) was developed as a second generation thrombolytic agent in an attempt to overcome some of the limitations to the intravenous application of streptokinase for coronary artery thrombolysis. Temporary protection of the active site on the plasminogen molecule by acylation allows APSAC to be given by rapid injection, confers semiselectivity for clot (at lower doses) and prolonged fibrinolytic action. These properties may simplify intravenous administration, improve coronary reperfusion response and reduce reocclusion potential. Clinical trials with APSAC, still ongoing, allow the following tentative conclusions: the efficacy of intravenous APSAC appears to be equivalent to that of intracoronary streptokinase, when given within 4 hours of the onset of symptoms of myocardial infarction, and superior to that of intravenous streptokinase, but it is easier to administer. Early APSAC therapy leads to reperfusion rates of 60 to 65% and patency rates of 70 to 80%. Early reocclusion rates (within 24 hours) appear to be as low as or lower than those obtained with other agents. Bleeding complications and allergic manifestations after APSAC are acceptably low and comparable with those of equivalent doses of streptokinase. The potential for mortality benefit after APSAC appears to be high and is undergoing additional study. Thus, APSAC therapy, which can be given by simple injection over 2 to 5 minutes, appears promising as a future first line approach to reperfusion therapy in acute myocardial infarction.