Articular cartilage have dual functions of shock absorber and bearing surface in a moving joint. Articular cartilage is avascular, so the chondrocytes in mature adult must receive their nourishment solely from synovial-fluid perfusion, and it is known that alteration of synovial-fluid perfusion causes degeneration of articular cartilage. Now, in orthopedic fields, the corrective cast immobilization and traction is in popular use. In order to study the cartilage changes induced by this long-term cast immobilization and traction, compression-immobilization and condylar resection of knee joint in rabbits were performed, and weekly histoiogic examinations of articular cartilage up to 5 weeks were followed. The observations were as follows: 1. Degenerative changes of articular cartilage were observed respectively with compression-immobilization and condylar resection, and the severity of the histologic changes appeared to be proportional to the duration of compression-immobilization and condylar resection. 2. Earlier degenerative changes of articular cartilage in condylar resection group than in compression-immobilization group were noted, and this earlier degenerative changes in condylar resection group suggests that hemarthrosis may play a role in cartilage degeneration. 3. Histologically unchanged calcific cartilage zone and mildly hypertrophied subchondral bone were noted in compression-immobilization group, but vascular invasion to calcific cartilage zone and subchondral osteoporosis were noted in condylar resection group.