Endocrine cells in the intrahepatic biliary tree were examined histochemically and immunohistochemically in human infants and adults, as well as in patients with hepatolithiasis. Endocrine cells were sparse but found rather constantly in normal infant livers as well as in adult livers. Almost all endocrine cells were of argyrophil cells or somatostatin-containing cells, and they were usually found in the extramural peribiliary glands in normal livers. On the other hand, in hepatolithiasis in which there were marked proliferation of the peribiliary glands and hyperplasia of surface-lining epithelia, many kinds of endocrine cells were seen in the extramural and intramural peribiliary glands, as well as in the lining epithelial layer. Furthermore, these endocrine cells were hyperplastic in the affected intrahepatic bile duct in two patients with hepatolithiasis. These data suggested that argyrophil cells and somatostatin-containing cells are physiologically present in the intrahepatic biliary tree, and many kinds of other endocrine cells newly appear and even proliferate in hepatolithiasis. These findings imply the participation of reported action of these hormones on bile flow in normal livers and hepatolithiasis.