In a randomised, controlled trial 2514 patients with suspected acute myocardial infarction received 100 mg intravenous alteplase (recombinant tissue plasminogen activator [rt-PA]) plus heparin within 5 h of onset of symptoms, and 2499 similar controls received placebo plus heparin. At 1 month the overall mortality rates were 7.2% and 9.8%, respectively, a relative reduction of 26% (95% confidence interval [CI] 11-39%). At 6 months the mortality rates were 10.4% (alteplase) and 13.1% (placebo), a relative reduction of 21% (95% Cl 8%-32%, p = 0.0026). 6-month mortality rates in patients with proven myocardial infarction were 12.6% and 17.1%, respectively (relative reduction 26%; 95% Cl 14-37%); this effect was similar for anterior (15.6% vs 21.2%) and inferior (7.7% vs 12.8%) myocardial infarction. 6-month mortality rates were lower in those treated with alteplase irrespective of other recognised cardiac risk factors. However, treatment with alteplase made no difference to subsequent cardiac events after one month (readmissions, reinfarctions, death) nor to treatment for angina or heart failure. Product limit estimates of one year mortality are 13.2% with alteplase and 15.1% with placebo. The corresponding figures for patients with an index diagnosis of myocardial infarction are 15.7% and 18.9%, a relative reduction of 16.9%.