OBJECTIVE The aim of this study was to compare the effects of the ACE-inhibitor lisinopril and the angiotensin II receptor antagonist losartan on insulin sensitivity in the treatment of non diabetic hypertensives. METHODS Twenty-five non diabetic subjects with mild to moderate hypertension, 11 females and 14 males, aged 44-63 years, after a 4-week wash-out period on placebo, were randomized to receive lisinopril 20 mg once daily or losartan 50 mg once daily for 6 weeks. Following another 4-week wash-out period, patients were crossed to the alternative regimen for further 6 weeks. At the end of the placebo and of the active treatment periods, blood pressure (BP) was measured (by standard mercury sphygmomanometer, Korotkoff I and V) and insulin sensitivity was assessed by the euglycaemic hyperinsulinaemic clamp technique. Glucose infusion rate (GIR) during the last 30 min of clamp and total glucose requirement (TGR) were evaluated. RESULTS Both lisinopril and losartan significantly reduced SBP (by a mean of 20.2 and 17.2 mmHg, respectively) and DBP (by a mean of 15.2 and 12.3 mmHg, respectively), with no difference between the two treatments. GIR, used as an indicator of insulin sensitivity, was significantly increased by lisinopril (+1.5 mg min(-1) kg(-1), P<0.05 vs baseline) but not by losartan (+0.42 mg min(-1) kig(-1), NS), the difference between the two drugs being statistically significant (P<0.05). TGR was increased by lisinopril (+7.3 g, P<0.05 vs baseline), whereas losartan did not significantly modify it (+1.9 g, NS). CONCLUSIONS In conclusion, with all cautions due to an absence in this study of a randomized placebo phase, our findings suggest that lisinopril improved insulin sensitivity whereas losartan did not affect it.