The purpose of this study was to analyse the effects of thrombolytic therapy with intracoronary streptokinase in patients with acute myocardial infarction. Five centres participated in the study, the Thorax center in Rotterdam (237 patients), the Academic Hospital of the Free University of Amsterdam (93 patients), the Zuiderziekenhuis in Rotterdam (61 patients), the Academic Hospital of the University of Limburg in Maastricht (123 patients) and the Academic Hospital of Leiden (19 patients). The study was conducted by the Interuniversity Cardiology Institute the Netherlands. A strategy aimed at early reperfusion, including acute coronary angiography and intracoronary administration of streptokinase, was compared to conventional therapy of myocardial infarction without acute angiography and without administration of fibrinolytic therapy. Patients were eligible for the study if admitted to the hospital within four hours after onset of symptoms and with electrocardiographic signs typical for acute myocardial infarction. Patients over 70 years of age and patients with enhanced risks of bleeding were excluded. A total of 533 patients were included in the study of which 264 were randomly allocated to conventional treatment and 269 to thrombolytic therapy. Informed consent was sought from patients allocated to thrombolytic therapy only. Final patency of the infarct related artery was achieved with intracoronary streptokinase (usually 250,000 U) in 198 out of 234 patients (85% ). In 98 patients angiography was preceded by intravenous infusion of streptokinase (500,000 U). Clinical course was better in the thrombolysis group, less patients had symptoms of cardiogenic shock or heart failure. Also, the incidence of ventricular fibrillation appeared to be lower in the thrombolysis group. Bleeding complications were mainly related to the angiography puncture site. Thrombolytic therapy led to a limitation of enzymatic infarct size, measured by cumulative release of alpha-hydroxybutyrate dehydrogenase (median 770 U/1 vs 1100 U/1 in the control group; p = 0.0001). Left ventricular ejection fraction measured by contrast angiography 10 to 40 days after admission was higher in the thrombolysis group (median 53% vs 47% in the control group, p = 0.0001). Furthermore, thrombolytic therapy improved one year survival (90% vs 84% in the control group; p = 0.03). However, thrombolytic therapy led to a higher incidence of non-fatal myocardial infarction during the first year (13% vs 5% in the control group; p = 0.001).