The authors make a review of the literature and of their personal experience about the possible mechanisms of action and the beneficial therapeutic effects of ursodeoxycholic acid in primary biliary cirrhosis. They postulate that owing to its hydrophilic properties, ursodeoxycholic acid is more efficiently absorbed by the ileum than the other bile acids, so replacing the other bile acids in the bile acid pool, and that ursodeoxycholic acid is less toxic for hepatocytes than the other bile acids accumulating in the plasma and is also a choleretic.