Nonsteroidal anti-inflammatory drugs (NSAID) are useful in the management of juvenile chronic arthritis (JCA) and efficacy has usually been compared with aspirin. The disadvantages of aspirin include the frequency of dosage, monitoring of salicylate levels and concern about Reye's syndrome. We have performed a single blind crossover study comparing naproxen 10 mg/kg/day, tolmetin 25 mg/kg/day and diclofenac 2 mg/kg/day in 28 children with seronegative JCA over 12 weeks. Clinical and laboratory assessments were made after 4 weeks of treatment on each drug. Clinical improvement was seen with all three NSAID compared to baseline after a 24-hour washout period, but statistical significance was reached in only 2 or 3 of the clinical parameters for each drug. Side effects were mild and typical of NSAID, but occurred less frequently with naproxen (5) and tolmetin (5) than with diclofenac (7). Thus the anti-inflammatory effect of all three drugs was confirmed with no significant differences between them in terms of efficacy and tolerance. Tolmetin 200 mg tablets are now only available in France and N. America, therefore naproxen or diclofenac are recommended as the first line of treatment in children with chronic arthritis over the age of 5.