The efficacy of proglumetacin , a new non-steroidal antiinflammatory drug, was assessed in 32 patients with rheumatoid arthritis. During treatment with 400-650 mg daily of proglumetacin over a period of 7-14 days, morning stiffness and side-effects were checked weekly or in severely ill patients daily. All patients but one completed the period of treatment. In spite of the short period of observation, a significant improvement was seen in the majority of cases (55%), while in 39% proglumetacin was not more effective than treatments before the admission to the study. In the group of patients treated for 14 days, morning stiffness parameters showed a significant improvement after 7 days and at the end of the period of study. Overall , only 3 patients referred side-effects: 1 case of transient headache and 2 cases of severe gastric pain. In our preliminary study, proglumetacin results to be effective as an antiinflammatory drug also in severe rheumatoid arthritis and safe for its low incidence of side-effects.