We undertook a dose-response study in Wistar rats to develop an animal model for methotrexate hepatotoxicity. Rats were given oral methotrexate in 300, 200, 150 and 100 m̈g/kg/day doses for variable lengths of time. The 300 m̈g/kg/day dose produced systemic toxicity; the animals needed to be killed early, and hepatotoxicity was not observed. The lower doses of methotrexate were tolerated for longer durations and were associated with hepatotoxicity in five of the five rats receiving 200 m̈g/kg/day, four of the five rats receiving 150 m̈g/kg/day and five of the five rats on 100 m̈g/kg/day. Within each treatment group the liver injury ranged in severity from focal necrosis of some zone 3 hepatocytes to confluent necrosis of zone 3. All five rats that received 100 m̈g/kg/day methotrexate for 6 wk showed continuing liver injury in the form of focal necrosis, cell lysis and enlarged Kupffer cells. In addition, three of the rats showed evidence of early hepatic fibrosis. We believe that this is the first experimental model in which oral methotrexate administration has been associated with hepatotoxicity. Further development of this model should provide valuable insights into the pathogenesis of methotrexate hepatotoxicity. (HEPATOLOGY 1991;14:906–910).