Cimetidine-induced liver injury has only very rarely been reported. Three patients are described who developed signs of hepatic damage after the institution of cimetidine therapy. Transient signs of acute liver failure were noticed in one patient. Histologically, a cytotoxic type of injury with centrilobular confluent and bridging portal-central necrosis, accompanied by a mixed mono- and polymorphonuclear infiltrate with signs of cholangiolitis in the portal tracts was observed in two patients, whereas a hepatocanalicular type of cholestatic hepatitis was noticed in another patient. It is proposed that the mechanism of cimetidine-induced liver injury may vary in different patients: it may be due either to a 'metabolic idiosyncrasy' because of the production of hitherto unknown toxic metabolites or to a hypersensitivity reaction.