The RBF was measured by means of the 133Xe washout method in seventy patients with cirrhosis. The average RBF in controls was 3.72 ml/g-min compared with 2.34 in the patients without ascites, 1.82 in the decompensated patients, 1.47 in the patients with azotaemia and 1.13 in the patients with additional oliguria. The RBF was not significantly correlated to changes in the systemic or portal haemodynamics. Likewise it was not correlated to any biochemical test of liver function except the serum albumin concentration (P less than 0.01). From the present results it can be concluded that a reduction in RBF in cirrhosis frequently is present before sodium and water retention is clinically evident and before laboratory proof of impairment of renal function, and that a subnormal serum albumin concentration may be a factor among several leading to renal hypoperfusion in cirrhosis.