We studied 73 patients with acute myocardial infarction (AMI) treated by percutaneous transluminal coronary angioplasty (PTCA) without thrombolysis (direct PTCA) and 52 patients with AMI treated by PTCA immediately after thrombolysis (PTCR + PTCA). The initial results, angiographic findings and preservation of ventricular functions of the direct PTCA group were compared with those of the PTCR + PTCA group. 1. The success rate of coronary recanalization was higher in the direct PTCA group than in the PTCR + PTCA group, but there was no statistical significance (89% vs 77%; p = NS). 2. Major complications occurred in 4.1% of the direct PTCA group and in 5.8% of the PTCR + PTCA group (p = NS). 3. The incidence of acute coronary reocclusion was higher in the PTCR + PTCA group than in the direct PTCA group (7.4% vs 22%; p less than 0.05). 4. Angiographic haziness at the dilated site following PTCA was seen more frequently in patients in the PTCR + PTCA group than in those of the direct PTCA group (43% vs 23%; p less than 0.05). 5. Patients with haziness at the dilated site had a significantly higher incidence of acute coronary reocclusion than did the patients without such haziness (28% vs 6.3%; p less than 0.05). 6. Left ventricular ejection fraction and regional wall motion were better preserved in the direct PTCA group than in the PTCR + PTCA group, but there was not statistical significance. It was suggested that direct PTCA is safe and can be performed with good success rates. It is superior to PTCR + PTCA in avoiding acute coronary reocclusion, and thus we supposed that the response of lesions to angioplasty may be altered by the administration of thrombolytic agents.