The authors participated in the European multicenter investigation, ESPRIT, organized by the Wellcome Research Laboratories. Thrombolytic treatment by intravenous tissue plasminogen activator was performed in 25 patients with early (less than 6h) myocardial infarction. The efficacy of the treatment was controlled by repeat coronary arteriography at 60 minutes, at 90 minutes and at 24 hours of the tpA treatment. The infarct related artery was reperfused in 9/25 patients at 60 minutes, in 16/25 at 90 minutes and 17/18 at 24 hours. Four patients died after unsuccessful treatment or reocclusion. In two patients significant bleeding occurred at the puncture site but no transfusion was required. No other untoward effect was registered. The left ventricular function did not change significantly during the first day of infarction. It is concluded, that tpA is a safe thrombolytic agent in myocardial infarction. Its thrombolytic efficacy is similar to that of streptokinase.