Insulin resistance and hyperinsulinemia are linked with essential hypertension. To clarify insulin sensitivity in Japanese essential hypertensive patients and the role of insulin resistance in these patients, a euglycemic hyperinsulinemic glucose clamp was applied in 17 essential hypertensive patients and 12 normotensive subjects. The mean glucose infusion rate was used as an indicator of insulin sensitivity (M value). This study revealed a significantly lower M value in essential hypertensive patients than in normotensive subjects. Increased plasma norepinephrine, renin activity, and aldosterone levels were observed after hyperinsulinemia for 120 minutes after glucose clamp in normotensive subjects and essential hypertensive patients. Urinary sodium excretion and fractional excretion of sodium were decreased in essent ial hypertensive patients as well as normotensive subjects during glucose clamp compared with the period before glucose clamp. No difference in the percent change was observed between essential hypertensive patients and normotensive subjects. These results indicate that selective insulin resistance with respect to glucose metabolism exists in essential hypertensive patients and that insulin action on renal sodium handling and pressor systems was maintained in these patients.