A primary association between hypertriglyceridemia and decreased glucose tolerance has been demonstrated in patients with hyperlipidemia or gout or both. Impaired tolerance was found in 72% of 25 patients with hypertriglyceridemia whereas only 12% of 25 patients with essential hypercholesterolemia had this abnormality. In 25 gouty patients, triglyceride levels were normal in six, and abnormal glucose tolerance was present in one of these. Nineteen of the group had hypertriglyceridemia and of these, 74% had decreased carbohydrate tolerance. The results indicate that abnormalities in triglyceride metabolism may be a fundamental factor in the pathogenesis of diabetes and that the presence of hypertriglyceridemia may be used to predict the presence of coexistent diabetes. Cholesterol levels, by themselves, are of little significance in this respect.