The pharmacokinetics after oral administration of 1,200 mg antipyrine and intravenous administration of 0.5 mg/kg indocyanine green have been investigated in 6 normal subjects and in 20 patients with chronic liver disease of varying etiology. Severe impairment of liver function associated with a decrease in serum albumin, elevation in serum bilirubin, or prolongation in prothrombin time correlated with a fall in the clearance of both drugs. The clearance of the two drugs correlated well in normal subjects and in patients with chronic liver disease. The presence of a surgical portacaval anastomosis was associated with a lower indocyanine green clearance for comparable clearance of antipyrine. The concept of functioning hepatic parenchymal mass is proposed as a common rate-limiting parameter for the elimination of the two drugs.