One major function of the liver is the uptake of endo- and xenobiotics from the bloodstream and their excretion into bile. The transport systems involved in hepatobiliary transport have been recently cloned and characterized at the molecular level and it is becoming clear that mutations and polymorphisms of individual transporter molecules underlie a variety of liver diseases. Furthermore, new research has shown that bile acids, whose function in digestion is long known, also behave as signal molecules in a variety of organs, including the intestinal and biliary epithelia, sinusoidal...