Increase of the aminotransferase levels in 53 patients treated with methotrexate (MTX) were analysed in a retrospective study. The mean dose of MTX was 7.46 mg/week (range 2.5-15 mg) during at least 30 weeks (mean time of MTX use 124 weeks). The aminotransferase levels were transitorily increased in 13 patients, always less than three times the upper limit of normal. Only in three patients the AST and ALT levels were persistently increased and lead to the drug discontinuation in two cases. These results showed that increase of aminotransferases was a frequent observation (24.5%) during the first two-three years of follow-up, without interference in the overall clinical management.