The effects of long-term lisinopril therapy on glucose tolerance and serum lipid profiles were investigated prospectively in 30 hypertensive patients: 15 with normal glucose tolerance and the remaining 15 with glucose intolerance. The levels of plasma glucose, serum lipids, and plasma glycosylated hemoglobin A1c were determined before and during long-term (6 months) therapy with lisinopril. A 75 g oral glucose tolerance test was performed before and during long-term lisinopril therapy. Lisinopril produced significant falls in both systolic and diastolic blood pressure in both patient groups during the long-term therapy. Neither fasting nor post-glucose-load venous plasma glucose levels were altered in either group of patients, and no patients with normal glucose tolerance developed diabetes mellitus during the study. There was no significant change in the insulinogenic index (delta IRI/delta BS at 30 min post-glucose load) in both patient groups. No significant changes in fasting levels of serum cholesterol, triglycerides, and HDL-cholesterol were observed in either group during long-term lisinopril therapy. Long-term lisinopril therapy does not compromise glucose or lipid metabolism in hypertensive patients. Lisinopril may have an advantage as an antihypertensive agent that can be given to hypertensive patients without concern that it might alter their serum lipid concentrations or impair glucose tolerance.