In a prospective study of aspirin therapy for 67 children with juvenile rheumatoid arthritis, we have found that (1) doses greater than 100 mg/kg/day of aspirin may be necessary to achieve therapeutic salicylate levels greater than 20 mg/dL; (2) no improvement in clinical remission rate is seen at salicylate levels greater than 30 mg/dL; (3) clinical toxicity to aspirin is of relatively low incidence (16%), and infrequently causes serious morbidity; (4) symptomatic SGOT elevations are common in the first three months after onset of therapy; and (5) these elevated SGOT levels generally return to normal despite continuation of therapy.