To answer the question of whether thrombolysis is a clinically useful approach in acute myocardial infarction, we initiated in May 1981 a randomized trial to compare a strategy aimed at early recanalization by intracoronary administration of streptokinase with conventional treatment in the coronary care unit. The primary objective was to study the effect of the intervention on mortality and morbidity after myocardial infarction. In addition, we analyzed the effect of attempted thrombolysis on infarct size and left ventricular function measured by various methods. The intake was completed in March 1985 after entry of 533 patients. The data presented in this report demonstrate that improved survival after early thrombolysis in acute myocardial infarction is indeed associated with a reduction of infarct size and with preservation of global left ventricular function. Furthermore, regional wall motion after thrombolysis appeared to be better than in the control group. The difference between the present study and the other randomized trials published thus far can be explained by differences in study design, by the shorter delay between the onset of symptoms and treatment, and by its larger size.