We compared acute hemodynamic, hormonal, and natriuretic responses to a single oral dose of captopril (50 mg) versus enalapril maleate (10 mg) administered to eight patients with biopsy-proved liver cirrhosis. Although the two angiotensin-converting enzyme (ACE) inhibitors lowered (p less than 0.05) blood pressure with no change in heart rate during the early postdose period, captopril produced a greater (p less than 0.05) hypotensive effect than did enalapril. Enalapril caused a greater (p less than 0.01 to 0.05) ACE inhibition than did captopril during the 2- to 48-hour postdose period. Plasma renin activity increased (p less than 0.05) with the two drugs and returned toward baseline by 12 hours after administration. Plasma aldosterone levels, elevated before drug administration, were decreased by the two drugs in a stepwise fashion, but the suppressive effect was greater (p less than 0.01 or p less than 0.05) after captopril than after enalapril. Natriuresis was greater (p less than 0.05) during the first 24-hour period after enalapril than after captopril. The findings indicate that the acute pharmacodynamic responses to the two ACE inhibitors differ in patients with liver cirrhosis. However, the mechanism(s) of the divergent effects of the two drugs and the clinical implications remain obscure from this single-dose study.