Twenty patients with mild or medium severe essential hypertension were treated with lisinopril (Prinivil), 20 or 40 mg resp. by the oral route per day. After six weeks of treatment the mean values of systolic pressure declined from 169 +/- 4.38 mm Hg to 149 +/- 3.96 mm Hg and the diastolic pressure from 108 +/- 0.99 mm Hg to 91 +/- 1.77 mm Hg. The differences were statistically significant. In 40% of the patients it was necessary to increase the daily dose of lisinopril to 40 mg. When this was used, the mean values of systolic pressure declined to 140 +/- 3.18 mm Hg and those of diastolic pressure declined to 85 +/- 1.43 mm Hg during the subsequent six weeks. The blood pressure of all investigated patients was within the range of reference values. The authors recorded a positive effect on the glucose metabolism in particular in patients with impaired glucose tolerance. The mean blood sugar levels during the second hour following glucose administration during the oGTT declined from 9.81 +/- 0.54 mmol/l before treatment to 7.28 +/- 0.79 mmol/l after 12 weeks of lisinopril treatment. The values of immunoreactive insulin after the mentioned intervals declined from 82.49 +/- 5.6 to 34.94 +/- 8.37 microM/ml. The investigated parameters of the lipid spectrum did not change after 12 weeks of treatment. The authors did not observe any marked side-effects of treatment.