Histological studies in male C57 black mice revealed a high incidence (39-61%) of osteo-arthrotic changes in the knee joint from about the 17th month of life. In animals of the same strain aged 15 1/2 months the incidence was only 19%. The incidence of gonarthroses in 16-month-old female mice was considerably lower (4%). In male mice aged 17-20 months, the oral administration of tribenoside in doses of 500 and 1,200 mg/kg weekly led to a significant (p less than 0.05) reduction in the overall arthrotic involvement. A possible relation between the effect of tribenoside and other anti-inflammatory agents on osteo-arthroses in the mouse and their influence on mucopolysaccharide metabolism in connective tissue is discussed. The incidence of the formation of gaps in the epiphyseal growth zones and of osteoporosis of the femur and tibia in the same strain increases distinctly with advancing age. Except in animals treated with the highest dosage tested, in which there was a significant decrease in the development of osteoporosis, tribenoside in the range of doses used had no influence on these skeletal changes.