Pathology of the intrahepatic bile ducts bearing calculi was examined with an emphasis on metaplasia in 22 cases of hepatolithiasis and in seven cases of normal livers. Normal livers contained few glandular elements within the bile duct walls and no metaplastic lesions or endocrine cells. In hepatolithiasis, a number of mucous glands resembling pyloric glands (pseudopyloric gland metaplasia) were seen within duct walls in all cases. The epithelial cells of the glands were positive for class III mucin with paradoxical concanavalin A staining which is known to be specific for pyloric glands. These cells were also positive for neutral, sialo- and sulfomucin to a variable extent. Intestinal metaplasia, including goblet cell and Paneth cell metaplasia, was found within duct walls and in covering epithelia in five (23%) cases. Endocrine cells, including argyrophil, argentaffin and gut hormone-containing cells were present in these metaplastic lesions in 13 (59%) cases. The occurrence of endocrine cells was closely associated with intestinal metaplasia, although there were a few endocrine cells in metaplastic pseudopyloric glands. These findings suggest that metaplastic lesions similar to the well-known metaplastic lesions in the gallbladder occur in the intrahepatic bile duct walls in hepatolithiasis. The appearance of metaplastic lesions and endocrine cells may be causally related to chronic inflammatory processes associated with hepatolithiasis.