The aim of the present study was to evaluate bone regeneration around nonsubmerged implants placed immediately in extraction sites in the canine mandible using a combination of synthetic hydroxyapatite (HA) and collagen membranes. Ten beagle dogs were used in this study. After the second and third mandibular premolars were extracted, hollow-screw implants were placed in the distal extraction sockets. In each animal, one site received no treatment (control site), while other defects received randomly 1 of the following treatments: grafting with porous HA in the peri-implant region, collagen membrane adapted to the implant cervical collar covering the peri-implant defects, or a combination of the 2 treatments, ie, HA grafting and membrane placement. After 4 months of healing, block biopsies were obtained and prepared for histologic analysis using the cutting-grinding technique. The histometric evaluation took into account the number of integrated screw threads, the extent of bone-to-implant contact, and the density of peri-implant bone. At sites covered by membrane alone or by membrane and HA, the number of integrated threads was statistically higher than sites treated only with HA. The extent of bone-to-implant contact was significantly different between treatments. However, the use of bioabsorbable materials did not significantly enhance peri-implant bone regeneration in immediate implantation. Schlagwörter: bioabsorbable material, bone regeneration, dental extraction, titanium dental implants