A follow-up study of 1,402 patients with a positive maximal treadmill stress test was made to evaluate the significance of angina during the test. Life tables were constructed and evaluated for significance of age, sex and work load at onset of angina. Coronary events (myocardial infarction, progression of angina and coronary death) were twice as frequent in subjects with angina and S-T segment depression as in those without angina. The increased incidence in 4 years held for all coronary events and was still doubled at 7 years for progression of angina and coronary death. The incidence of coronary events was more than twice as great when the angina was induced by a light work load (4 metabolic equivalents = METS) as when it was induced by a heavy work load (8 to 9 METS). Men aged 41 to 50 years having angina during exercise testing had a 3-fold greater incidence of coronary events and a 4-fold greater incidence of myocardial infarction compared with their counterparts who had S-T segment depression alone. In this study, angina during exercise testing identified 85% of true positive tests for coronary artery disease, whereas S-T depression alone identified only 64% of such tests. Thus, angina during exercise testing increases the sensitivity of the test and identifies cohorts of subjects at high risk for subsequent coronary events.