The levels of hepatic GSH [glutathione] in animals intoxicated with bromobenzene were studied. A marked decrease of hepatic GSH was observed in poisoned rats. Such decrease was prevented by previous administration of lead nitrate, an inhibitor of DMES [drug-metabolizing enzyme system]. In the rats treated with lead nitrate alone a rise in hepatic GSH was observed. Such protection was further observed by histological examination. The mechanism of protection exerted by lead nitrate against bromobenzene intoxication is discussed.