The aim of this study was to evaluate the effect of captopril on carbohydrate metabolism in diabetic patients with essential arterial hypertension. Sixteen patients with non-insulin-dependent diabetes mellitus and hypertension were studied. Captopril was employed in different doses, and where patients receiving 100 mg/day remained hypertensive, hydrochlorothiazide 50 mg/day was added. Treatment was maintained for 90 days in 14 patients, 2 being excluded because of side effects. Basal blood pressure was normalized in 8 patients (57%) with captopril alone, and in 6 patients (43%) following the addition of hydrochlorothiazide. Basal glucose levels were not altered. Oral glucose tolerance tests performed during captopril treatment showed a lower glucose response, without changes in the insulin response. There was significant weight loss during the study. We conclude that captopril appears to be a safe treatment in essential hypertension associated with non-insulin-dependent diabetes mellitus, producing no deleterious effects on metabolic control.