Two hundred and seventy patients, under 71 years of age and suffering from a less than 4 h infarction diagnosed according to clinical and electrocardiographic criteria, were included: two 90-patient groups were randomized and then treated with either anistreplase (30 mg iv over 5 min) or alteplase (10 mg bolus injection + 5000 IU heparin bolus injection, followed by 90 mg alteplase over 3 h), and compared with a consecutive control series of 90 patients treated with streptokinase (1.5 million U over 1 h). Intravenous heparin and aspirin (250 mg day-1) were then prescribed routinely. The three groups were comparable as regards age (55.2 +/- 10 years), male/female ratio (10.4), the site of the infarction (42% anterior, 55% inferior) and initial clinical seriousness (Killip I = 90%, II = 8%, III = 2%). The patients were thrombolysed in 17 community hospitals, and then referred to a university hospital with catheterization facilities. An efficacy score was determined, based on four parameters: two obtained from coronary angiography and left ventriculography performed on day 6 +/- 2 (N = 252) (asynergic score and patency of the infarct-related artery), one from Tl-tomography performed at rest (infarct size) and one from radionuclide angiography (global left ventricular ejection fraction) performed between day 15 and day 21 (N = 242). The score (range: 0-24 per patient) was 17.8 +/- 6.4 for alteplase, 17.7 +/- 6.0 for anistreplase and 18.1 +/- 6.0 for streptokinase respectively (NS).(ABSTRACT TRUNCATED AT 250 WORDS)