The purpose of this investigation was to analyse, after 6 years of clinical trials, the findings obtained from biopsies of infrabony defects in man treated by grafts of hydroxyapatite. Filled extraction sockets in miniature swine treated in a similar manner with apatite were also studied. Light microscope analysis showed bone neoformation around and in the neighbourhood of grafted apatite fragments with the presence of osteocytes, osteoblasts and a normal peripheral connective tissue without inflammatory reaction. These results demonstrate the biocompatibility of the implanted apatites accompanied by a normal fibrogenesis and a seeming osteogenesis.