The study objective was to establish a safe and efficacious dose of ketoprofen in children with JRA during a 4-week, open-labeled, non-controlled trial. Initial dosage was 100 mg/m2/d, gradually increased up to 200 mg/m2/d, not to exceed 320 mg/d. One patient was removed from the study due to hematuria. Clinical improvement was observed in 50% or more of the patients in 8 of the 15 indices assessed. Statistical improvement was detected in the number and severity of joints with pain on motion, the duration of morning stiffness, and the time required to travel 50 feet (p less than .035). Significant laboratory changes included decreases in the mean hemoglobin and hematocrit, and increases in ESR and BUN (p less than .03). Twenty patients experienced a total of 39 adverse effects and of these, 6 were judged to be attributable to ketoprofen. These preliminary data suggest ketoprofen's efficacy and safety is comparable to that of other nonsteroidal antiinflammatory drugs.