The Thrombolysis in Myocardial Infarction (TIMI) trial Phase I was designed to compare the efficacy and side effects of intravenous recombinant tissue-type plasminogen activator (rt-PA) and intravenous streptokinase (SK) in patients with acute myocardial infarction (AMI). As previously reported, rt-PA led to a reperfusion rate of 62% of totally occluded coronary arteries compared with 31% for SK (p less than 0.001). This study was not designed to determine if intravenous thrombolytic therapy decreases the mortality of AMI; however, the findings in these patients after 1 year of follow-up do permit certain insights into the impact of early reperfusion and reocclusion on the clinical course of patients with AMI. The mortality rate at 6 and 12 months was not significantly different in patients treated with rt-PA compared with SK (7.7% and 10.5% rt-PA vs 9.5% and 11.6% for SK). The frequency of recurrent AMI, coronary artery bypass grafting (CABG) and percutaneous transluminal coronary angioplasty (PTCA) was similar in the 2 treatment groups. There was no significant difference in 6- and 12-month mortality or in the rate of recurrent AMI in patients who received thrombolytic therapy before compared with after 4 hours of the onset of AMI symptoms. When the results were analyzed on the basis of the patency of the infarct-related artery, irrespective of thrombolytic agent used, for those patients with patent arteries 90 minutes after the initiation of therapy, there was a trend toward a lower 6-month (5.6% vs 12.5%) and 12-month mortality (8.1% vs 14.8%) (p = 0.07).(ABSTRACT TRUNCATED AT 250 WORDS)