Data of 52 patients, 29 women and 23 men aged 32-68 years (mean age 47 years) with essential hypertension, participating in three open therapeutic trials with either enalapril, lisinopril, or perindopril were evaluated to assess the effects of angiotensin-converting enzyme (ACE) inhibition on glucose and lipid metabolism. The 75-g oral glucose tolerance test (oGTT) was performed, and plasma glucose and insulin levels, as well as total cholesterol, high-density lipoprotein (HDL)-cholesterol, and triglycerides levels were determined before and after the 8- to 12-week treatment. Minor differences in the blood pressure (BP)-lowering effect and metabolic response were obtained with the ACE inhibitors studied; only lisinopril improved glucose tolerance significantly; blood lipids were not changed by any drug. The entire patient population showed only a slight reduction in 1-h postload glucose after treatment. More obvious improvement in glucose tolerance was evident in hypertensive patients who were glucose intolerant and/or insulin resistant (GI/IR, 53.8% of all), however. This subgroup also showed a slight but not significant increase in HDL-cholesterol and a decrease in triglycerides levels. Only a slight change or no change in plasma glucose, insulin, and lipid values was noted in hypertensive patients with normal glucose tolerance (NGT) and insulin sensitivity. These favorable effects were expressed only after ACE inhibitor monotherapy, but not when hydrochlorothiazide was added. The results indicate that a lack of stratification of hypertensive patients with regard to glucose tolerance or insulin sensitivity could be a confounding factor in evaluation of metabolic effects of ACE inhibitors.