Indomethacin in pharmacological doses was given to rabbits with papain-induced degenerative arthrosis of the knee. The cartilage lesions healed between the 35th and the 70th day of the experiment. The healing was unaffected by indomethacin. However, autoradiographs showed a significantly reduced 25SO4 uptake in the articular cartilage of the animals receiving the indomethacin in both arthritic and control knees.