ECG monitoring during treadmill exercise testing was performed in a prospective series of 105 consecutive patients with intermittent claudication scheduled for peripheral vascular surgery. ECG monitoring during the exercise test was useful in predicting perioperative cardiac complications. In 55 patients with evidence of coronary artery disease by history and ECG obtained at rest, a strong association (p less than 0.001) between an ischemic response to exercise testing and the occurrence of perioperative cardiac events was observed. ECG monitoring during the exercise test also revealed previously unsuspected ischemia or arrhythmias in six of the remaining 50 patients and predicted perioperative cardiac problems in four of these six. An ischemic response to low-level treadmill exercise testing probably indicates advanced coronary artery disease and offers valuable predictive information when a revascularization procedure is considered for the relief of intermittent claudication.