To compare the effects of two thrombolytic agents, streptokinase and recombinant tissue-type plasminogen activator (rTPA) with early heparinization, on left ventricular function, coronary patency and reinfarction rates, bleeding complications, and short- and long-term mortality, we studied 122 patients with acute myocardial infarction prospectively. All of them fulfilled the standard criteria for thrombolytic therapy. One group (n = 63) received 1,500,000 units of streptokinase over 1 hour, and one group (n = 59) received 100 mg of rTPA over 3 hours. Baseline data showed no significant differences between the streptokinase and rTPA groups. Results of predischarge studies 10 to 14 days after infarction revealed that there was no difference in left ventricular ejection fraction between the two groups (48.3% in the streptokinase group and 49.9% in the rTPA group; p = 0.67). The patency rate of the infarct-related artery tended to be higher in the rTPA group compared with the streptokinase group (77% vs 57%, p = 0.19). In-hospital spontaneous bleeding occurred after streptokinase in seven patients (11.1%) and after rTPA in eight (13.6%; p = 0.89). One patient had intracranial bleeding after rTPA and died 13 hours later. The early mortality rate within 30 days of acute myocardial infarction was 5 of 63 (7.9%) for the streptokinase group and 2 of 59 (3.4%) for the rTPA group (p = 0.49). During the 19.3-month follow-up period, reinfarction occurred in seven patients (11%) in the streptokinase group and in three (5%) in the rTPA group (p = 0.3). The mortality rates were 10 of 63 (16%) and 3 of 59 (5%), respectively (p = 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)