Thirty elderly, mildly hypertensive patients were enrolled for a single-blind, randomised cross-over placebo controlled trial in which placebo and lisinopril (20 mg/day before breakfast) were given for 4 and 8 weeks, respectively. A wash-out period of 3 weeks between placebo and lisinopril was observed. In each patient a euglycaemic glucose clamp with simultaneous indirect calorimetry allowed us to determine whole body glucose disposal and substrate oxidation. Changes in morning SBP and DBP were also determined. Lisinopril vs. placebo significantly improved whole body glucose disposal (40.4 +/- 0.4 vs. 30.3 +/- 0.4 mumol/kg LBM x min; P < 0.01), non-oxidative glucose metabolism (18.1 +/- 0.7 vs. 10.9 +/- 0.6 mumol/kg LBM x min; P < 0.01) and fasting plasma potassium levels (4.8 +/- 3 vs. 4.4 +/- 0.4 mmol/l; P < 0.05). SBP (175 +/- 3.3 vs. 160 +/- 3.0 mm Hg; P < 0.001) and DBP (106 +/- 2.3 vs. 95 +/- 2.0 mm Hg; P < 0.001) were significantly reduced by lisinopril administration. After ACE inhibition, fasting plasma potassium levels correlated with the decline in mean arterial BP (r = -0.71; P < 0.006). In conclusion, lisinopril administration reduces arterial BP and improves insulin sensitivity in elderly hypertensive patients.