Using freeze-fracture techniques, we have examined the changes in the morphology of the tight junctional network around the canalicular lumen of the hepatocytes in rat liver after experimental bile-duct ligation. The more or less regular belt of parallel strands formed by the tight junctions around the canalicular lumen of normal hepatocytes is changed after extrahepatic obstruction. A more irregular network is formed withe a reduced number of strands which also extend more in an abluminal direction with formation of irregular loops. Striking changes are seen at the gap junctions: the small patches normally situated within the tight junctional network become less numerous; at some canaliculi they are even absent; also the larger gap junctional areas normally present in deeer abluminal extensions of the lateral cell membrane become hard to find or are even absent. This altered tight junctional pattern suggests an increased permeability so that the pathway of intercellular escape of biliary constituents towards the blood stream in cholestasis becomes as plausible as transhepatocytic regurgitation. The disappearance of the gap junctions would result in a lack of intercellular communication and uncoupling of liver cells, which may lead to a more individual behaviour of adjecent hepatocytes, explaining the heterogeneity in canalicular changes in cholestasis.