The purpose of this study was to investigate the possibility of applying hydroxyapatite ceramics as endodontic-endosseous implants. The upper medial incisors of 3 monkeys (Macaca fuscatae) were used. To prepare the implant cavity, the teeth were extracted and drilled from the apex by steel burns under water-cooling. Then, dense hydroxyapatite implants, 10mm in length, 2mm in maximum diameter and 1/20 tapered, were inserted into the cavity to have the implant project 3-4mm above the apex. When the teeth with the implants were replanted, the bone around the apex was removed. The teeth were splinted to the neighbouring teeth for 1 month. Five months after the operation, the specimens were taken out and fixed by 10% formalin alcohol. They were embedded in polyester resin and undecalcified sections were prepared. The sections were stained with toluidine blue and observed under light microscope. RESULTS 1) At 5 months, no ankylosis between the tooth and the surrounding alveolar bone was observed. 2) There was newly formed hard tissue which extended from the cementum, on the surface of the implant. 3) Fiber bundles were observed around the implants which connected the newly formed hard tissue to the surrounding bone tissue. The results suggest that the application of hydroxyapatite ceramics as an endodontic-endosseous implant is effective.