Twelve white adult rabbits weighing 3000-4000 grams were used in this study. They were anesthethized with i. v. sodium pentobarbital.In one group, non-intracranially penetrating bone defects (about 5.0×5.0×1.5mm) were made in the frontal bone bilaterally. Hydroxyapatite and tricalciumphosphate composite (HTC) plugs of the same shape and size as the defects were inserted and covered with pedicled periosteum, free periosteum, or soft tissue only. Specimens of tissue were collected for histopathological examination 3 months later. The specimens were cut into 10μm thick sections and stained with hematoxylin and eosion for light microscopic studies.In the second group, HTC plugs of the same size (about 5.0×5.0×1.5mm) were placed on the frontal bone (onlay grafting) and covered as in the first experiment and examined in the same way.Macroscopic and microscopic examinations revealed firm contact between bone and HTC in all of the first group (bone defect group) and in the bones covered by pedicle periosteum in the second group. Firm contact between periosteum and HTC was observed in both groups. No infection or foreign body reaction occured. Three monthes later no invasion of osteoblasts from bone to composite was observed.Our results suggest that HTC has excellent and reliable biocompatibility with bone and periosteum.