Several studies report that essential hypertension is associated with hyperinsulinemia. This condition may depend on enhanced pancreatic insulin secretion and/or a decreased MCR of the circulating hormone. Twenty-five nonobese glucose-normotolerant patients with primary hypertension were divided into 5 groups, each consisting of 5 subjects. Each group was submitted to continuous 120-min double infusion of different doses of insulin (group I, 0.025; II, 0.05; III, 0.1; IV, 0.2; V, 0.4 U/kg.h) and glucose (I, 2; II, 3.5; III, 6; IV, 8; V, 10 mg/kg.min). The same procedures were applied to 25 healthy normotensive volunteers. Basal and steady state plasma levels of glucose, insulin, and C-peptide were significantly (P less than 0.05 or less) higher in hypertensive patients than in control subjects of all groups. The MCR of insulin (milliliters per kg/min) at all insulin-glucose infusion rates was significantly (P less than 0.05 or less) lower in hypertensive than normotensive subjects. Despite the significantly higher steady state plasma insulin levels in hypertensives, the MCR of glucose (milliliters per kg/min) was significantly (P less than 0.05 or less) lower in hypertensive than normotensive subjects. These results suggest that an altered insulin removal may contribute to the hyperinsulinemia found in the essential hypertensive subjects. In addition, a defect in insulin-stimulated glucose uptake which persists at supraphysiological insulin concentrations is confirmed in this population.