A total of 111 patients, aged 35 to 60, were examined. Of those, 97 had survived transmural or large-focal myocardial infarction (MI) 1-2 years before the study. The patients were divided into groups according to MI localization and the number of affected coronary arteries. Coronaro- and ventriculography, echocardiography (sectoral scanning), the computer-assisted treadmill exercise test were performed in all the patients. Exercise tolerance in post-MI patients was shown to be related to coronary circulation and unrelated to left-ventricular myocardial contractility at rest. The analysis of ST variation, particularly ST rise, as the only criterion for the assessment of the results of exercise testing demonstrated its moderate sensitivity in relation to the diagnosis of multiple coronary arterial lesions (MCAL) in post-MI patients. The informative value of the test increases if other parameters, particularly exercise tolerance, are assessed as well. Low tolerance combined with computer evidence of a positive test is in most cases indicative of MCAL, whereas with high tolerance in the absence of electrocardiographic ST changes MCAL would be unlikely.