Diclophenac sodium, Voltaren, has been tested against indomethacin and placebo in a four-week double-blind between-patient trial in 182 patients with rheumatoid arhritis. The ameliorating effect of Voltaren on the usual clinical parameters was comparable to that of indomethacin, while no significant changes were observed in the placebo group. Side effects during treatment with Voltaren and indomethacin appeared mainly form the gastrointestinal tract and from CNS. While side effects from the gastrointestinal tract were similar in the two groups, side effects from the CNS appeared significantly less frequent during treatment with Voltaren than during treatment with indomethacin. No skin reactions, diarrhoea or gastrointestinal bleeding were observed in either group. Long-term studies are needed to establish the place of Voltaren in the treatment of rheumatoid arthritis.