Twenty-nine children with juvenile rheumatoid arthritis were studied to determine the safety and efficacy of methotrexate therapy. The initial dose of methotrexate averaged 7.1 mg/m2/wk and was given as a single, oral weekly dose or as three divided doses, each separated by 12 hours. Current antiinflammatory medications were continued; 25 of 29 children had had lack of efficacy, and 8 of 29 had toxic effects, with one or more prior drugs such as intramuscularly or orally administered gold, hydroxychloroquine, or D-penicillamine. Intolerable corticosteroid dependency or toxic effects were present in 18 of 29 cases. Methotrexate-treated patients were examined monthly; minimum treatment duration required to assess efficacy and toxicity was 6 months. The range of treatment duration was 8 to 39 months (mean 18.5 months). Efficacy was assessed by comparing pretreatment versus posttreatment fever and rash, swollen-joint counts, articular indexes, duration of morning stiffness, functional class, hemoglobin levels, and platelet counts. Treatment with methotrexate effectively controlled fever and rash in 83% of children with systemic juvenile rheumatoid arthritis, reduced morning stiffness by 63%, eliminated recalcitrant joint restriction in 48%, and reduced numbers of swollen joints and swelling indexes by 46% and 52%, respectively. No significant toxic effects were observed. Juvenile rheumatoid arthritis of long duration, or with major erosions, was more likely to be refractory to methotrexate therapy. We recommend earlier consideration of methotrexate in place of other slow-acting antirheumatic drugs for juvenile rheumatoid arthritis not responding well to usual therapy. Future studies should address potential methotrexate toxic effects in the lungs and reproductive system, as well as outcome after discontinuation of methotrexate treatment.