Enalapril maleate (MK-421), a nonmercapto-containing angiotensin converting enzyme (ACE) inhibitor, is converted in vivo to enalaprilat (MK-422), the active diacid. We evaluated serum profiles and urinary excretion of oral enalapril maleate in patients with renal disease (group I, creatinine clearance less than 3 ml/min, patients undergoing dialysis, n = 10; group II, creatinine clearance 10 to 79 ml/min, n = 9) compared with healthy subjects (group III, creatinine clearance greater than 80 ml/min, n = 10). Group I received a 10 mg dose during a day while not receiving dialysis and a 10 mg dose 1 hour before dialysis 2 weeks later. Groups II and III received a single 10 mg dose. Blood samples and urine were collected for 48 hours. Impaired renal function resulted in elevated serum and plasma concentrations of enalapril maleate and decreased excretion rates and urinary recovery of enalapril maleate and enalaprilat. The data suggest an apparent increase in the extent of metabolism of enalapril maleate to enalaprilat or an increase in nonrenal elimination of unchanged enalapril maleate in renal disease compared with normal health. Enalaprilat was dialyzable.