This study investigated the relationship between urinary sodium excretion and liver function, as assessed by the aminopyrine breath test (ABT) and conventional parameters, in 62 patients with cirrhosis kept on a constant salt diet. Urinary sodium excretion was related non-linearly to the ABT (r = 0.76). Less significant correlations were observed to the Child-Pugh score (r = -0.65), cholinesterase (r = 0.58), bilirubin (r = -0.56), albumin (r = 0.51) and prothrombin time (r = 0.49). When patients were arbitrarily divided into 6 groups according to the ABT, sodium excretion balanced the sodium intake up to a 50% reduction in ABT. In groups with more than a 50% reduction sodium retention occurred. When patients were grouped according to the Child-Pugh score, urinary salt output was balanced in patients with scores of 5 and 6 and decreased in patients with scores greater six. However, the change in sodium output from normal salt excretion to sodium retention was less pronounced in patients grouped according to the Child-Pugh score than in patients grouped according to the ABT. The results suggest a non-linear relationship between the impairment in hepatic and renal function in cirrhosis. They are compatible with the concept of a threshold of hepatic function necessary to maintain normal renal function.