1. Techniques are described for homografting intact or partly digested hyaline cartilage or isolated chondrocytes on to cancellous bone in rabbits. 2. Material which had been cooled to and thawed from -79 degrees Centigrade either in the presence or absence of the protective substance dimethyl sulphoxide was grafted in the same way. In control experiments samples were boiled before grafting. 3. Necropsies were performed at intervals varying from two to twenty-six weeks later and the graft sites were removed, fixed and decalcified. Paraffin sections were stained histologically. 4. Freshly isolated chondrocytes or chondrocytes which had been frozen in the presence of dimethyl suiphoxide formed new matrix within two weeks and did not succumb to a homograft reaction. By the sixth week they had become aligned in columns surrounded by well stained matrix. There were signs oferosion by invading capillaries and osteoblasts, but no lymphocytes were seen. By the twelfth week invasion by trabeculae of newly formed bone was well advanced and by the twenty-sixth week the grafts were difficult to find although there had been no sign at any stage of an immunological reaction. 5. New matrix was also formed in homografts of hyaline cartilage which had been treated with papain or with papain and collagenase. After freezing in the presence of dimethyl sulphoxide, small areas ofthe grafts seemed to contain living cells which had formed new matrix. Other areas were disintegrating. 6. The homografts of intact cartilage showed a variety of appearances suggesting that the old matrix was gradually leached out and that chondrocytes liberated 7. Intact or partly digested cartilage which had either been frozen without dimethyl suiphoxide or boiled disintegrated and was rapidly replaced by bone after grafting. 8. When specimens of partly digested cartilage or isolated chondrocytes were homografted On to sites denuded of cartilage on the articular surface of the rabbit humeral head, nodules of fresh cartilage were formed. They were embedded in fibrous tissue derived, presumably, from marrow cavities opened up at the time of operation.
