Eighteen patients (nine girls, nine boys) with systemic onset juvenile rheumatoid arthritis (SO-JRA) treated with methotrexate (MTX) for a mean period of 18 months (range 6-41 months) were analysed to evaluate the safety and efficacy of MTX in this disease subtype. The MTX dose ranged from 2.5 to 15 mg/week with a mean cumulative dose of 684.9 mg/patient at the last follow-up visit. Systemic features were severe in 10 patients before MTX was started. None of these patients showed systemic features at the last follow-up visit. Sixteen patients (89%) showed improvement in both the active joint count (from a mean of 12.0 to 1.3 joints/patient) and function class (from a mean of 3.0 to 1.3) while receiving MTX. Eleven patients (61%) showed a significant decrease in the erythrocyte sedimentation rate (>50% of the initial value), an improvement in anaemia (haemoglobin >2 g) and reduced thrombocytosis (platelets 2 x 10[5]). Of the patients receiving corticosteroids, three patients (20%) were able to discontinue prednisone and the dose was reduced to less than 50% of the initial dose in seven patients (47%). At these doses of MTX, no gastrointestinal, hepatic or haematological toxicity was encountered and none of the patients withdrew because of toxicity or lack of efficacy. This report suggests that MTX is an effective and safe treatment in controlling systemic and articular features in this subtype of JRA.