The acute effects and pharmacokinetic properties of an angiotensin converting enzyme (ACE) inhibitor, ramipril, and its potent active diacid metabolite, ramiprilate, were investigated. Hypertensive patients with impaired renal function (IRF; n = 6) and with normal renal function (NRF; n = 5) were studied. The terminal half-life of ramiprilate in IRF was longer than that in NRF. The peak plasma concentrations of ramipril and ramiprilate in IRF were higher than those in NRF. The area under the plasma level-time curves of ramipril and ramiprilate in IRF were greater than those in NRF. A significant inverse correlation was found between creatinine clearance and area under the plasma level-time curve.