90 patients were enrolled into this preliminary multicentre study of the efficacy and safety of 30 units intravenous anisoylated plasminogen streptokinase activator complex (APSAC) compared with placebo in patients with acute myocardial infarction. 45 patients received APSAC and 45 placebo; the groups were similar for age, weight and site of infarction. There were significantly more women treated with APSAC (p less than 0.02). The mean time to treatment was 3.3 hours after symptoms of myocardial infarction for APSAC and 3 hours for placebo. The 30-day mortality was 7 patients in the placebo group and 1 in the APSAC group (p = 0.058). Adverse events were generally minor and were of similar overall frequency in both groups. There were more haemorrhagic events with APSAC, from which all patients recovered, and more cardiovascular events with placebo including 2 deaths from cardiogenic shock. APSAC showed a trend towards a reduction in 30-day mortality. Experience from this study has led to the initiation of the APSAC in myocardial infarction multicentre mortality study (AIMS).