To assess the indication for percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass grafting (CABG), we studied 93 patients with angina pectoris but without myocardial infarction. All patients had significant stenosis (greater than 50%) in at least one coronary artery, including the left anterior descending artery. Fifty-eight patients received medical treatment (Group I), 12 had PTCA (Group II) and 23 had CABG (Group III). Findings of coronary angiography, treadmill exercise tests and dipyridamole perfusion scintigraphy as well as the frequency of cardiac events during follow-up were assessed in each group. 1. Coronary angiography revealed 1 vessel disease in 38% of the patients in Group I, 58% in Group II, and 13% in Group III; 2 vessel disease in 33%, 25% and 61%; and 3 vessel disease in 29%, 17% and 26%, respectively. 2. Exercise duration with the treadmill test was 4.7 min in Group I, 4.0 min in Group II and 3.7 min in Group III. ST depression (greater than or equal to 1 mm) was induced in 75%, 83% and 95%, respectively. Exercise duration improved from 4.0 to 6.0 min after PTCA and from 3.7 to 4.5 min after CABG. Exercise-induced ST depression also became less frequent; from 83% to 25% after PTCA and from 95% to 32% after CABG. Dipyridamole perfusion scintigraphy showed reversible defects in 86% of the patients in Group I and in all patients in Groups II and III. Reversible defects were observed in 17% of the patients after PTCA and in 21% after CABG. 3. During a mean follow-up period of 26 months, cardiac deaths occurred in one patient (2%) in Group I and 2 (7%) in Group III. Nonfatal cardiac events (myocardial infarction and unstable angina or those necessitating revascularization--late PTCA or CABG) were observed in 12 patients (21%) in Group I, 4 (24%) in Group II and 10 (36%) in Group III. Anginal attacks at least once weekly remained in 12% of the patients in Group I, 19% in Group II and 14% in Group III at the last follow-up. In conclusion, PTCA and CABG appear to be effective methods for improving ischemia and exercise tolerance. However, preventive PTCA and CABG may not be indicated in patients with mild angina, because the prognosis is also excellent in medically-treated patients with angina but without myocardial infarction or left main coronary artery disease.