Hepatic morphological abnormalities were examined in rats whose bile ducts had been either cannulated and then obstructed or irreversibly ligated for 5, 10, 15 and 28 days or longer. Throughout the experiment most of the morphological changes observed in the cannulated group were comparable to those in the ligated group. Portal inflammation and marginal bile duct proliferation were noted with the same frequency in both groups. Biliary obstruction for 15 days or more led to cirrhosis. After 28 days obstruction, five out of six cannulated rats and four out of six ligated animals respectively developed cirrhosis. The development of cirrhosis was progressive and associated with ascites. It is concluded that in the rat the morphological sequelae of long term cholestasis induced by either cannulation and obstruction or ligation of bile ducts are similar and are accompanied by cirrhosis. The advantages of this experimental model for the study of human cirrhosis are discussed.