Absorption of bile acids by diffusion occurs in all parts of the intestine whereas the active transport is only located in the terminal ileum. Absorption of ursodeoxycholic acid (UDCA) in the small intestine is slow and incomplete due to the poor solubility of this bile acid. After oral administration, UDCA competitively inhibits the absorption of endogenous bile acids in the ileum. This effect leads to changes in bile acid metabolism which may be related to its beneficial effect in cholestatic diseases.