Twenty male diabetic patients (age range, 40-60 years) with normal autonomic function were studied to determine the prevalence of silent myocardial ischemia on exercise as well as ambulatory electrocardiography. The presence and extent of silent myocardial ischemia was also correlated with the severity of atherosclerotic coronary artery disease as determined by coronary angiography. A cohort of 20 matched non-diabetic patients were also included in the study. Silent myocardial ischemia was detected in 50% of the diabetic patients on exercise electrocardiography and in 35% on ambulatory electrocardiography compared with 10% and 5% in non-diabetics by the two methods, respectively (P < 0.01 and P < 0.05, respectively). On exercise testing in diabetic patients, silent myocardial ischemia was detected in 64% of the patients with three-vessel disease, 50% of the patients with two-vessel disease and 20% of the patients with one-vessel disease whereas in non-diabetic patients silent myocardial ischemia was detected in only 18% of the patients with three-vessel disease (P < 0.05) and in none of the patients with two- or one-vessel disease. On ambulatory electrocardiography, only patients (both diabetic and non-diabetic) with three-vessel disease manifested silent myocardial ischemia. Total ischemic burden was similar in both the diabetic and non-diabetic patients. We conclude that silent myocardial ischemia occurs in diabetic patients with coronary artery disease more frequently even in the absence of autonomic dysfunction and the prevalence of silent myocardial ischemia is higher in patients with severe degree of coronary artery disease.