Normal values for simple and rate-corrected measures of the duration and dispersion of electrocardiographic (ECG) repolarization during treadmill exercise were obtained in 94 clinically normal men, and the behavior of these measures during ischemia was examined in 79 men with catheterization-proven disease or with stable angina, all of whom had normal resting ECGs. Temporal measures of repolarization, exemplified by QTc, were found to be moderately sensitive for disease only when highly specific criteria were derived from data at peak exercise heart rates that were significantly higher in normal subjects than in patients; sensitivities of rate-corrected measures declined markedly when criteria were derived from matched heart rate data in normal subjects. In contrast, the standard deviation of the mean measured J-point to T-wave peaks across the V1 to V6 precordial leads (SD-SoTm), a measure of precordial dispersion of repolarization, was unrelated to exercise heart rate in normal subjects; SD-SoTm exceeding the 95% value at matched intraexercise heart rates in normal subjects was found at peak exercise in 38% of men with coronary disease, including some patients with otherwise false-negative standard exercise test responses.