Fifty-three male volunteers who had undergone coronary artery bypass surgery were randomized to a medically supervised exercise program (N = 28) or to usual community care (N = 25). They were tested initially and at one year with exercise tests for thallium scintigraphy, maximal oxygen uptake, and electrocardiography. Approximately one third of the patients had signs and/or symptoms of ischemia consistent with incomplete or unsuccessful revascularization. Over the year there were five dropouts, but no major complications occurred. The exercisers attended an average of 82% of the sessions (three times a week) and trained at 80% of their maximal heart rate. Both the exercisers with and those without angina had significant increases in estimated and measured oxygen uptake and significant declines in submaximal and resting heart rate. There was a trend toward improved thallium scans in the exercised patients with angina.