An oral water load of 20 ml per kg body weight was given to 9 patients with hepatic cirrhosis and 11 healthy controls. Urinary output, free water clearance, and plasma concentrations of arginine vasopressin, angiotensin II and aldosterone were determined before and three times during the first 4 h after loading. In the cirrhotic patients urinary output was significantly lower after loading than in the control subjects, mainly because of a lower free water clearance, and, in contrast to the healthy controls, the cirrhotic patients did not have natriuresis after water loading. No differences were found between patients and controls in arginine vasopressin, angiotensin II, aldosterone, or creatinine clearance. It is concluded that patients with well-compensated cirrhosis of the liver have an impaired ability to excrete sodium and water. This phenomenon does not seem to be due to increased arginine vasopressin secretion, activation of the renin-angiotensin-aldosterone system, or a decreased glomerular filtration rate.