This article describes the effects on patients treated with intracoronary streptokinase during acute myocardial infarction and long-term follow-up. The mortality and the incidence of cardiac events were assessed during a follow-up period of 35 +/- 5 months. Coronary artery bypass grafting was undertaken in 37% of the patients. Hospital mortality was 11%, (n = 8); none of these deaths was due to myocardial rupture. The postdischarge mortality was 10%; three of these patients experienced sudden death. Serial assessment of left ventricular function in 35 patients showed an increase of angiographic ejection fraction prior to intervention from 50 +/- 4% to 58 +/- 12% (p = 0.005) 36 +/- 53 days later. Gated-blood pool imaging after 16 +/- 7 months (n = 35) and 32 +/- 9 months (n = 31) revealed no change in ejection fraction. Angina pectoris recurred in four of the 35 patients. We studied a historical comparison group, that consisted of 66 patients, who were treated at the same institution prior to the advent of intracoronary intervention techniques; this group was followed for 48 +/- 9 months. Baseline clinical and angiographic parameters were comparable in the two groups. Coronary artery bypass grafting was performed in only 18 of these patients. Mortality during hospitalization and postdischarge was not significantly different in the two groups. Ejection fraction decreased significantly in the comparison group from the first to the second evaluation and remained unchanged during the follow-up period. We conclude that no major adverse effects were associated with intracoronary streptokinase infusion over a long follow-up period. This may be related to the high frequency of coronary artery bypass surgery following reperfusion.