Renin-angiotensin system plays a prominent role in the sodium and water homeostasis. In addition, activation of renin-angiotensin system frequently occurs in patients with cirrhosis and ascites. Theoretically, administering of angiotensin converting enzyme inhibitors can enhance sodium and water retention in cirrhotic patients with ascites. In this study, we evaluate the role of low-dose captopril on renal function changes, renal plasma flow and hemodynamics in patients with cirrhosis and ascites. Fifty patients are randomly assigned to receive captopril or placebo for 14 days. Renal functions, renal plasma flow, plasma renin activity, plasma aldosterone concentration and systemic and hepatic hemodynamics are measured before and after treatment. Our results indicate that placebo administration did not affect any of the parameter measured in this study. The finding that low-dose captopril significantly increases plasma renin activity suggests that the dose used in this study effectively blocks the enzyme activity. However, low-dose captopril does not affect renal plasma flow, renal functions and systemic and hepatic hemodynamics. Results in this study demonstrate that inhibition of angiotensin converting enzyme alone may not improve sodium and water retention in cirrhotic patients with ascites.