Patients who received coronary arteriography at the clinical units because of severe angina or unstable angina, with or without antecedent myocardial infarction, were asked to participate in the study. A total of 2,013 eligible patients who refused randomization and 422 who were ineligible on the basis of angiographic findings were asked to participate in the follow-up registry. The remaining patients were then randomized, 914 to CABG and 915 to PTCA, between August 1988 and August 1991. Baseline data included the clinical profile, 12-lead electrocardiogram, and information on coronary angiographic features, angina and functional status, medications, risk factors, and quality of life. Initial revascularization was performed within two weeks after randomization. Angiograms (baseline and sub study directed at 1 year and 5 years), and ECG's are interpreted by respective core laboratories. Scheduled multiple stages of PTCA were counted as a single procedure. New interventional devices, such as stents, were not used during the initial revascularization. Follow-up visits were conducted at the clinics at weeks four through fourteen after study entry and at one, three, and five years, with telephone contacts at six months and two and four years. The importance of risk factor modification was emphasized throughout the study to the patients and their primary physicians. The primary end point was mortality from all causes.