Myocardial damage in acute myocardial infarction is a time-dependent process. Thrombolytic therapy effectively opens the coronary artery, restores coronary blood flow and prevents ongoing necrosis. We examined the effect of very early thrombolytic therapy (including prehospital administration) in a consecutive group of 510 patients with myocardial infarction on the following factors: mortality, complications and the preservation of left ventricular function. The treatment was given to 89 at home (time delay to treatment 1.2 +/- 0.6 h) and 421 in hospital (2.0 +/- 1.0 h). Twelve patients died in hospital and major hemorrhage occurred in 10. The arterial patency rate in 416 patients who underwent coronary angiography 6 days later was 82%. Infarct size measured by left ventriculography was determined by the area at risk, the delay time until the initiation of thrombolytic therapy, the total duration of ischemic pain and the degree of restoration of arterial blood flow. We conclude that early thrombolytic therapy, particularly prehospital management, is feasible and safe and reduces infarct size and mortality. A further decrease in the delay to initiation of treatment and more effective thrombolytic therapy will further decrease mortality and myocardial damage.