In 15 patients with cirrhosis of the liver, the pressures in a systemic artery, in the inferior vena cava and the portal vein, flows in the portal vein and the hepatic artery, and oxygen content and acid-base balance in the arterial, portal and hepatic venous blood were studied during operation before and after the construction of an end-to-side portacaval shunt. Portal pressure decreased from 23 to 13 millimeters of mercury. Portal flow increased from 660 mililiters per minute to the liver to 1,300 milliliters per minute through the shunt. Hepatic arterial flow increased from 230 to 480 milliliters per minute, but this did not fully compensate for the loss of portal blood flow to the liver. Accordingly, total hepatic blood flow was reduced. There was also a decrease in the oxygen transport to the liver, but in spite of this, there was no change in the oxygen content in the hepatic vein nor any production of acid metabolites. Possible implications of these findings on the preoperative investigation of patients with portal hypertension are discussed.