A multicentre randomised trial including 87 patients admitted for acute myocardial infarction compared the effects of a single intravenous bolus of an anisoylated plasminogen streptokinase activator complex (APSAC) 30 units with those of heparin treatment on haemostasis during the first 4 days after treatment. In the APSAC group, a rapid and significant reduction in fibrinogen, plasminogen and alpha 2-antiplasmin was observed, associated with an increase of fibrin(ogen) degradation products, reflecting a strong systemic lytic activity. None of these parameters were significantly modified by heparin, but the anticoagulant effect was apparent as assessed by the activated partial thromboplastin time. The systemic fibrinolysis induced after different regimens of streptokinase infusion demonstrated that an intravenous bolus of APSAC 30U was as potent as streptokinase 500,000 or 1,500,000IU administered intravenously over 45 minutes and definitely more fibrinolytic than intracoronary infusion of streptokinase 250,000IU. Despite the demonstrated fibrin specificity of the drug at a low dose, a high dose of APSAC (30U intravenously) induced an important systemic lytic state for at least 12 hours.