To determine whether ACE inhibitor other than captopril improves insulin sensitivity in patients with essential hypertension, we measured insulin sensitivity to glucose utilization using SSPG method in 10 lean hypertensive subjects before and after chronic cilazapril treatment (1.5 +/- 0.2 mg/day, 15.6 +/- 2.1 weeks). The results were compared with those obtained in 10 healthy control subjects. SSPG obtained by insulin sensitivity test was significantly higher in hypertensive subjects, indicating a lower insulin sensitivity than in controls. After cilazapril treatment, SSPG reduced significantly to the level which was statistically not different from control subjects. Hyperinsulinemia diminished after treatment, while no significant change of blood glucose was observed during oral glucose tolerance test in hypertensive subjects. Plasma HDL cholesterol increased by cilazapril treatment. Cilazapril treatment has beneficial effect in the reversal of insulin resistance in patients with essential hypertension.