In TIMI I, to assess the relative thrombolytic activity and side effects of intravenous recombinant tissue-type plasminogen activator (rt-PA) versus intravenous streptokinase in patients with acute myocardial infarction. In TIMI II, to assess whether intravenous rt-PA given in the early hours of acute myocardial infarction should be followed by percutaneous transluminal coronary angioplasty (PTCA).