We evaluated the dynamic response of renin, aldosterone, and vasopressin to intravenous water loading (20 ml 5% glucose/kg b.w.) in 12 children (aged 7-18 years) with postinflammatory liver cirrhosis after hepatitis B virus (HBV) infection. All of the patients had early-stage liver cirrhosis; according to Child's classification, nine patients had group A; three, group B cirrhosis. A group of 17 children with chronic persistent hepatitis served as the control. The diagnoses were confirmed in all of the patients by liver biopsy. The patients followed a diet containing 3 mmol NaCl/kg/day, maximum 100 mmol per day for 6 days. Water loading was performed in recumbency over approximately 45 min. Renin, aldosterone, and vasopressin, assayed by radioimmunoassay (RIA), were determined before, 1 h, and 5 h after starting the water load. Prestudy hormone levels were within normal range in both groups. Renin and aldosterone concentration change patterns were similar in both groups and characterized by suppression of hormone activity caused by central volume expansion and recovery to prestudy levels after 5 h. However, the pattern of change of vasopressin concentrations differed in the control and study groups. In contrast to that of the controls, volume expansion did not suppress vasopressin in the group with liver cirrhosis. We conclude that failure to suppress vasopressin activity after central volume expansion may be one of the early mechanisms responsible for water-electrolyte imbalance in liver cirrhosis in children.