We have evaluated the effect of enalapril in the prevention of restenosis after percutaneous transluminal coronary angioplasty by a randomized trial conducted on 95 patients. The treatment group (n = 46) received enalapril 10 mg/day besides aspirin with calcium blockers, beginning 24 hours before coronary angioplasty. The conventional medical treatment group (n = 49) received only aspirin and calcium blockers. Enrollment required the presence of angina pectoris and successful dilatation of all significant coronary narrowings. All patients were followed up for at least 6 months. Restenosis was identified by symptoms and exercise testing and confirmed by angiography. The incidence of angiographic restenosis was 34% in the enalapril group and 31% in the conventional treatment group. Long term angiotensin converting enzyme inhibition with enalapril in a dose of 10 mg per day does not prevent restenosis after coronary angioplasty.