Indomethacin retard and piroxicam were compared in an open, randomized, parallel study in the treatment of osteoarthritis. Improvement of the symptoms of the disease was highly significant for both drugs. There was no statistical difference between the two drugs in terms of efficacy. Number and duration of side effects were significantly lower with piroxicam than with indomethacin retard. Piroxicam was administered once a day. Indomethacin retard was always (43% of the cases) or sometimes (14%) given twice daily.