The natural origin of hydroxyapatite (HA) derived from pig bones (Polish patent No.P-359 960 pending from 5th May 2003) was histologically examined for its biocompatibility following implantation into mouse muscles. The implanted ceramic was encapsulated by well vascularized connective tissue and very slowly resorbed by multinucleated cells. This material did not elicit an immune reaction and adjacent bones were unaffected. This ceramic could be safely used as a filling material alone, or as a composite graft.