There has been a tremendous amount of scientific progress in our understanding of the molecular mechanisms of transport processes in the liver within the last few years. Cloning of various members of organic anion and cation transporters has provided the necessary tools to study their regulation under physiological and pathophysiological conditions and has advanced our knowledge about bile formation. Mutations of various hepatic organic anion transporters have been identified in humans as hereditary defects leading to the heterogenous syndrome of progressive familial intrahepatic cholestasis...