The impact of age on hospital mortality, incidence of major hemorrhagic events and transfusion requirements was examined in 756 patients with acute myocardial infarction enrolled in the Thrombolysis in Myocardial Infarction (TIMI) Phase I, open label studies and the TIMI Phase II pilot study. The mortality rate significantly increased with age and was 3.5%, 11.5% and 12% in patients less than 65, 65 to 69 and 70 to 76 years of age, respectively (p less than 0.001). Logistic regression analyses selected female gender, diabetes mellitus, extensive coronary artery disease, history of congestive heart failure, continuing chest pain immediately after recombinant tissue-type plasminogen activator (rt-PA) administration, low systolic blood pressure at the time of admission and advanced age as variables predictive of in-hospital death. The incidence of major hemorrhagic events among patients not undergoing cardiac surgery during hospitalization was 8.7%, 14.5% and 24.7% in patients aged less than 65, 65 to 69 and greater than or equal to 70 years, respectively (p less than 0.001). The majority of hemorrhages were secondary to cardiac catheterization or puncture wounds. Variables related to a major hemorrhagic event included protocol, age, rt-PA dose/kg body weight and elevated diastolic blood pressure on admission. Of five intracranial bleeding events, three occurred in patients greater than 65 years. Transfusion requirements significantly increased with age (p less than 0.001). Reperfusion status at 90 min in the TIMI Phase I and open label studies A to C was similar in the three age groups studied and ranged from 60% to 71%.(ABSTRACT TRUNCATED AT 250 WORDS)