Cholangiocytes-the epithelial cells which line the bileducts-are increasingly recognized as importanttransporting epithelia actively involved in the absorptionand secretion of water,ions,and solutes.Thisrecognition is due in part to the recent development ofnew experimental models.New biologic concepts haveemerged including the identification and topography ofreceptors and flux proteins on the apical and/orbasolateral membrane which are involved in the molecularmechanisms of ductal bile secretion.Individually isolatedand/or perfused bile duct units from livers of rats andmice serve as new,physiologically relevant in vitromodels to study cholangiocyte transport.Biliary treedimensions and novel insights into anatomic remodeling ofproliferating bile ducts have emerged from three-dimensional reconstruction using CT scanning andsophisticated software.Moreover,new pathologicconcepts have arisen regarding the interaction ofcholangiocytes with pathogens such as Cryptosporidiumparvum.These concepts and associated methodologiesmay provide the framework to develop new therapies forthe cholangiopathies,a group of important hepatobiliarydiseases in which cholangiocytes are the target cell. Cholangiocytes-the epithelial cells which line the bileducts-are increasingly recognized as importanttransporting epithelia actively involved in the absorption and secretion of water, ions, and solutes. This histognition is due in part to the recent development of new experimental models .New biologic concepts haveemerged including the identification and topography of receptors and flux proteins on the apical and / or basolateral membrane which are involved in the molecular mechanisms of ductal bile secretion. Indoors individually isolated and / or perfused bile duct units from livers of rats and mouse serve as new, physiologically relevant in vitromodels to study cholangiocyte transport. Biliary treedimensions and novel insights into anatomic remodeling of proliferating bile ducts have emerged from three-dimensional reconstruction using CT scanning and customized software. Moreover, new pathologic conditions have arisen regarding the interaction of cholangiocytes with the pathogens such as Cryptosporidium hummum. The conc epts and associated methodologiesmay provide the framework to develop new therapies forthe cholangiopathies, a group of important hepatobiliary disorders in which cholangiocytes are the target cells.