Coronary artery disease is the most frequent cause of death among adult diabetic patients.1 Myocardial ischemia is often silent in these patients,2 and 33 to 42% of them do not experience chest pain during myocardial infarction.3 Absence of pain has been attributed to autonomic neuropathy,3-5 which is fairly common in patients with diabetes. Silent myocardial ischemia,2 infarction4-6 and sudden cardiac death6,7 occur most often in patients who also have autonomic dysfunction. Diabetic patients dying of painless myocardial infarction have morphologic features typical of diabetic neuropathy in the autonomic nerve fibers supplying the heart.4 However, not all patients with florid diabetic autonomic neuropathy have painless myocardial infarction. 5 The mechanism of painless myocardial infarction in diabetic patients, therefore, remains unclear and it is not known whether autonomic dysfunction is responsible for the lack of pain. No systematic study has examined the differences in autonomic functions between diabetic patients with painful and painless myocardial infarctions. Therefore, this study investigated the autonomic functions in 14 diabetic patients with myocardial infarction, 7 of whom had no chest pain during infarction.