To investigate the mechanism of exercise-induced ST elevation in previous anterior myocardial infarction, exercise body surface mapping was performed on 22 patients with anterior myocardial infarction. ST elevation was compared with the findings of exercise radionuclide ventriculography and exercise thallium-201 myocardial perfusion imaging. ST-segment was quantified by the integral of ST-segment voltage. The maximal value of ST segment integral out of the 87 leads on the body surface was defined as ST max. The percent of change in ST max after exercise was closely correlated to the decrease in ejection fraction (r = 0.76). Furthermore, 9 of the 12 patients with increased ST max after exercise had exercise-induced regional wall motion abnormalities mainly in the apical and anterolateral segments, while other 10 patients without increased ST max did not (p less than 0.01). There was no difference in % change of ST max a) between anterior reversible defect (+) group and the (-) group; b) between inferior reversible defect (+) group and the (-) group; c) between single vessel (isolated left anterior descending artery stenosis) group and the multivessel group. This fact indicated that exercise-induced ST elevation did not result from the exercise-induced myocardial ischemia of the infarctional segment or the remote non-infarctional segment. We concluded that exercise-induced ST elevation in previous anterior myocardial infarction is mainly due to the aggravation of anterior wall motion abnormalities induced by exercise.