The effect of the converting enzyme inhibitor lisinopril on renal and cardiac hemodynamics was studied in patients with moderate to severe primary hypertension, in a multicenter, double-blind, randomized clinical trial comparing the antihypertensive effect of lisinopril (LIS) and nifedipine (NIF). After a 2 week placebo run-in period, 15 patients were randomized in a 2:1 ratio to receive either LIS (20-80 mg q.d., n = 10) or NIF (20-40 mg b.i.d., n = 5). LIS significantly reduced blood pressure (BP) without changing heart rate or cardiac output. LIS significantly increased renal blood flow; glomerular filtration rate (GFR) was not changed. It can be concluded that LIS is an effective antihypertensive agent with a favorable renal hemodynamic profile.