Mediators of inflammation modulate the extent of hepatocellular necrosis following the administration of hepatotoxins. Since corticosteroids interfere with the generation of some of these mediators they might thus protect against the hepatotoxicity of drugs such as acetaminophen. To test this hypothesis mice were pretreated with two doses of prednisolone (10 and 20 mg/kg i.p., 17 and 2 h, respectively) prior to a hepatotoxic dose of 375 mg/kg acetaminophen and the metabolism and toxicity of acetaminophen were assessed. Twenty-four hours after acetaminophen the activity of ALT in plasma (737 vs. 6775 U/l) and the extent of hepatocellular necrosis (4 vs. 45% necrotic hepatocytes) were significantly lower in prednisolone-pretreated mice. Prednisolone pretreatment resulted in decreased covalent binding of the toxic metabolite in vivo and an increased urinary excretion of glutathione-derived conjugates of acetaminophen, indicating an enhanced detoxification of the reactive metabolite by glutathione. Nevertheless, hepatic glutathione was less depleted by acetaminophen in the prednisolone group, indicating an increased capacity to resynthesize glutathione. This was confirmed in experiments with diethyl maleate which depletes hepatic glutathione without causing cell injury. Following the administration of diethyl maleate to fed and fasted mice, hepatic glutathione was depleted to the same extent after 45 min, but was significantly higher after 2.5 h in prednisolone-pretreated mice. The present results indicate that prednisolone increases the capacity to replete depleted hepatic glutathione stores in mice.