The effect of glycosaminoglycan polysulphate as medication for osteoarthritis was studied in an experimental model of osteoarthritis induced by periodic immobilization of rabbit knees. In a pilot experiment with 5 weeks of continuous immobilization there were indistinct differences between treated and control groups. In the main study the right knees of 31 rabbits were immobilized five times for a period of one week at 4-week intervals, followed by 8 weeks without immobilization. The development of osteoarthritis was evaluated by mobility measurements, from radiographs and from the macroscopic appearance of the tibial and femoral joint faces at the end of the experiment. After each removal of the immobilization splint the treatment group showed significantly better mobility of flexion (14 degrees-37 degrees), but at the end of the follow up both groups had normal mobility to flexion. The radiographic stages of osteoarthritis after the fourth week of immobilization and at the end of the experiment were slight-moderate in the treatment group, while the controls had moderate and moderate-severe stages. After the assessments of macroscopic appearance, the tibial and femoral joint facies showed slight and slight-moderate osteoarthritis in the treatment group, while the controls had moderate osteoarthritis. This study indicates that glycosaminoglycan polysulphate may inhibit the development of osteoarthritis.