The aim of this study was to assess the incidence of early reocclusion after therapeutic reperfusion of coronary arteries in acute myocardial infarction. Seventy four patients underwent intracoronary thrombolysis and 133 patients had immediate coronary angioplasty. The success rates were 70 per cent and 86 per cent respectively (p less than 0.01) and the degree of residual stenosis was 77 +/- 13 percent and 25 +/- 15 per cent respectively (p less than 0.001). The patients in whom coronary reperfusion was successful, 52 after in situ thrombolysis, 48 after angioplasty alone, and 66 after combined angioplasty and intravenous thrombolysis, underwent coronary arteriography 24 to 36 hours later. Reocclusion was asymptomatic in 46 per cent of cases (13/28) and its prevalence was 16.9 per cent: 25.5 per cent for the right coronary compared with 12.8 per cent for the left anterior descending (p less than 0.05) and 11.7 per cent for the left circumflex artery; reocclusion occurred in 8.6 per cent of patients treated before the 3rd hour compared with 22.9 per cent of patients receiving treatment after the 3rd hour (p less than 0.05). The incidence of reocclusion was 17.3 per cent after intracoronary thrombolysis and 16.7 per cent after angioplasty (angioplasty alone 18.7 per cent; associated with thrombolysis 15.2%). The degree of residual stenosis was nil after intracoronary thrombolysis and 16.3 per cent after angioplasty when the stenosis was insignificant, and 20.5 per cent and 18.8 per cent respectively with stenotic lesions greater than 50 per cent.