Functional renal failure accompanying advanced cirrhosis of the liver carries a grave prognosis. Seven patients with the hepatorenal syndrome and five patients with decompensated cirrhosis of the liver without renal failure were studied by the xenon Xe 133 washout technique. Mean renal blood flow and its cortical component were decreased in both groups compared to normal transplant donors, but to a significantly greater degree in hepatorenal syndrome. In hepatorenal patients, intra-arterial infusion of subpressor doses of dopamine hydrochloride improved the angiographic appearance of the renal cortical vasculature and the cortical blood flow rate. Urine flow rate and glomerular filtration rate did not consistently improve with 12- to 24-hour intravenous infusions, although two patients survived, temporally related to the study. These patients had shown signs of liver function recovery.