Negative U-waves (NU) are not infrequently observed during anginal attacks. Correlations of prevalence of NU and coronary arteriographic findings were observed in 84 patients whose 12-lead electrocardiograms were obtained during anginal attacks. The left anterior descending coronary artery (LAD) was involved in 27 patients, the left circumflex artery (LCX) in 23 and the right coronary artery (RCA) in 34. NU were observed in 44 (52%) of 84 patients with angina; 17 (63%) with LAD, 13 (57%) with LCX, and 14 (41%) with RCA stenosis. The majority (91%) of patients with angina-induced NU had severe (greater than or equal to 90%) coronary stenosis. In the patient group with LAD stenosis, NU were most frequently observed in V4 (59%) greater than V5 (56%) greater than V6 (37%) greater than V3 (33%), while more frequent in V6 (52%) greater than V5 (48%) in the group with LCX stenosis, and in III (29%) greater than a VF (24%) greater than V6 (21%) in the group with RCA stenosis. Thus, the location of the stenosed vessel could be predicted electrocardiographically from the sites of the NU. Coronary revascularization was performed in 10 patients (59%) with LAD stenosis, in nine (69%) with LCX stenosis and in eight (57%) with RCA stenosis. Both anginal attacks and NU resolved after successful coronary revascularization. We concluded that NU proves a highly predictive parameter for detecting and locating significant coronary artery stenosis.