The effects of vasopressin and of its analogues on liver function, and their possible mechanisms of action, are poorly understood. This study was designed to assess the effect of triglycyl-lysin-vasopressin on liver function, evaluated by two quantitative tests independent of liver blood flow, i.e., indocyanine green intrinsic hepatic clearance and galactose elimination capacity. Indocyanine green intrinsic hepatic clearance and galactose elimination capacity were determined before and after administration of 2 mg triglycyl-lysin-vasopressin to (respectively) 10 and 12 patients with cirrhosis. Eighteen additional patients with cirrhosis were studied before and after infusion of placebo. No significant variation in either test was observed in placebo-treated patients. A significant decrease in indocyanine green intrinsic hepatic clearance, averaging 22%, was observed in patients receiving the drug (p = 0.04). Conversely, galactose elimination capacity remained unchanged after the drug. These results are compatible with the hypothesis that the drug produced a preferential decrease in perfusion in functioning areas of the liver, with relative maintenance of blood flow in non-functioning areas.