The purpose of this study was to assess the osseous response to implanted particles of an anorganic xenograft bone mineral. Bio-Oss, in six patients with severely resorbed alveolar ridges. The observation period varied between 9 and 44 months; in five of six patients, long-term bo ne regeneration around the implants was observed. Histolgoic examination of biopsy material obtained from the graft area showed Bio-Oss particles still present in all patients after the varying observation periods. This raises the question whether Bio-Oss may be regarded as a resorbable material, as previously reported.