BACKGROUND: Methotrexate has become a standard second-line agent for the treatment of sarcoidosis. Because sarcoidosis has a high frequency of liver involvement, we routinely perform a liver biopsy after each cumulative gram of methotrexate therapy in patients with sarcoidosis in whom we plan to continue therapy. METHODS: Following a previously described protocol for methotrexate therapy, we have performed 100 liver biopsies on 68 patients with chronic sarcoidosis at our institution. On the basis of the liver biopsy results, we identified the following 4 groups: sarcoidosis (47 cases), toxic effects of methotrexate (14 cases), hepatitis C (2 cases), and normal liver tissue (37 cases). RESULTS: We found no difference among the groups in terms of age, weight at time of biopsy, the number of patients receiving corticosteroids at the time of biopsy, cumulative dose of methotrexate, race, or sex. The 14 cases of toxic reactions to methotrexate included 5 patients who had undergone 1 or more previous liver biopsies in which the results did not show toxic effects. We found a significant difference between groups for levels of alkaline phosphatase and asparate aminotransferase at the time of starting (or restarting) methotrexate therapy (analysis of variance, P<.05). This finding was also true for the liver function tests performed at the time of the biopsy (analysis of variance, P<.05). The highest values were for those whose biopsy findings showed sarcoidosis. CONCLUSIONS: Toxic reactions to methotrexate eventually occurred in more than 10% of patients with sarcoidosis treated for more than 2 years with methotrexate. Because of hepatic involvement owing to sarcoidosis, results of serial liver function tests were not useful in determining which patients would have this reaction to methotrexate.