Methotrexate therapy was evaluated in 30 children with juvenile chronic arthritis according to the type of onset. The systemic form seemed less responsive than the ANA positive form with a polyarticular course or polyarticular onset. The clinical improvement, particularly in the ANA positive polyarticular course was confirmed by a significant decrease in the values of the ESR. Side effects occurred in 12 patients and consisted of gastrointestinal upset, mouth ulcers, slight leucopenia and elevated transaminases. They led to discontinuation of the treatment in only one child. Concomitant therapy could be stopped in 50% of the patients with an ANA positive polyarticular course, but remained necessary in the two other groups. These results indicate a differential effect of MTX therapy according to the type of JCA.