A 15 week double blind controlled trial of methotrexate and lO-deazaaminopterin for the treatment of rheumatoid arthritis (RA) was performed in 26 patients. Significant improvement in all measured clinical parameters was observed in the two patient groups. The drugs were well tolerated; only one patient (10- deazaaminopterin) withdrew from the study because of side effects. It is concluded that, in the context of this relatively short clinical trial, 10-deazaaminopterin is at least as beneficial as methotrexate in the treatment of RA.