The simultaneous measurement of wedged hepatic venous pressure and portal venous pressure at 11 and 28 days following common bile duct and intrahepatic bile duct obstruction reveals a significant elevation of the portal pressure at 28 days which is due primarily to increased presinusoidal resistance to portal blood flow. Portal venograms performed prior to sacrifice revealed moderate narrowing of the portal vein radicles and delayed emptying at 11 days and severe morphological alterations at 28 days. These results confirm the findings of other investigators and help to explain why the hemodynamic alterations occur so rapidly in obstructive jaundice, well before the development of significant biliary cirrhosis.