ABSTRACT— Intrahepatic cholestasis in paraquat poisoning in man has been thought to be secondary to extensive bile duct injuries, though its exact mechanism remains unsettled. We have examined liver biopsy specimens from two cases of paraquat poisoning. Case 1 (fatal) presented severe intrahepatic jaundice, and liver biopsy showed centrilobular cholestasis with extensive bile duct loss. Ultrastructurally, dilatation of bile canaliculi with decrease of microvilli and thickening of pericanalicular ectoplasm was found in the hepatocytes. Case 2 (alive) showed mild liver dysfunction without jaundice. While liver biopsy showed nonspecific reactive changes with intact bile ducts and ductules, electron microscopy disclosed dilatation of bile canaliculi with decrease of microvilli and thickening of pericanalicular ectoplasm in the hepatocytes, suggesting that damage to the bile secretory apparatus in the hepatocytes develops irrespective of extensive bile duct loss. These findings suggest that bile secretory apparatus in the hepatocytes as well as biliary epithelial cells could be a target of paraquat or its metabolites.