Cultured chondrocytes were bound to hydroxyapatite (HA) and implanted in surgically created bone defects in the ulna of the rabbit. Chondrocytes were obtained from the iliac crest cartilage of the rabbit and were cultured on the HA block for two weeks before implantation. Scanning electron micrographs showed that pores of the HA surface and the inside of the block were filled with cultured cells. After cultivation for two weeks, the expression of chondrocyte-specific characteristics was confirmed in these cells by an implanted diffusion of chondrocyte-specific characteristics was confirmed in these cells by an implanted diffusion chamber experiment. The HA without chondrocytes served as a control. At two weeks postimplantation, proliferating chondrocytes were observed on the surface and in the inside pores of the HA-chondrocyte blocks but not the HA controls. At four and six weeks postimplantation, in the central region of the implants, there was a significant increase in the amount of bone formation in the HA with cultured chondrocytes. At 13 weeks post-implantation, the implants were partially resorbed and completely enveloped in lamellar bone, including bone marrow.