We evaluated the effectiveness and the tolerability of a new non steroidal antiinflammatory drug (NSAID), nabumetone (1 g/daily for at least 8 days), in 20 patients (10 males and 10 females), 4 with rheumatoid arthritis and 16 with osteoarthritis. During the treatment we observed a progressive reduction of pain and swelling with improvement of articular movements. Our results showed an appreciable effectiveness of nabumetone treatment in 75% of patients. Excluding two patients with transient mild side effects (gastric and cutaneous symptoms), the tolerability has been satisfactory.