A histological comparison of rabbit knee joints subjected to continuous compression, and relief of contact by resection of one femoral condyle, revealed common changes in articular cartilage, consisting in loss of matrix metachromasia and nuclear staining characteristics. Those joints subjected to compression showed hypertrophy of the subchondral bone while the joints relieved of contact demonstrated local osteoporosis. Persistence of the zone of calcified cartilage characterized the compressed joints, while the resected joints showed early subchondral vessel invasion and loss of the zone of calcified cartilage and tidemark.