This study was undertaken to histologically, clinically and radiographically evaluate the sequence of healing following implantation of bovine demineralized bone powder (DBP) into severe, spontaneous periodontal defects in beagle dogs. Eight dogs with documented severe periodontitis were treated surgically following initial debridement. One quadrant in each arch was treated with conventional flap surgery and the others were treated with surgery followed by DBP implantation. Animals received postoperative debridement and clinical and radiographic evaluation. Two dogs were sacrificed at 1, 3, 6 or 12 months postoperatively, and the jaws were evaluated histologically. Clinically, DBP was well tolerated by recipients. No evidence of localized inflammatory response or delayed hypersensitivity reaction was noted. Significant reductions in gingival inflammation were noted in both experimental and control sites at 1 month postoperatively compared to preoperative scores. Equivalent periodontal pocket reduction was noted between test and experimental sites and remained significant at 12 months. Radiographically, no differences were noted in the rate of bone loss between control and test sites. Histologic evaluation demonstrated the presence of DBP at 1 month following implantation, but the material was replaced with new bone by the next sacrifice period. Periodontal ligament fibers of standard orientation were seen extending from DBP-induced bone to the root surface by 1 month after implantation. An intact epithelial attachment appeared to be present 1 month after the implantation of DBP. No differences in root surfaces were detected between test and control groups. Ankylosis was a rare finding, noted equally between test and control sites. DBP did not appear to predispose to external root resorption. In later stages, histologic evidence of advancing periodontitis was noted equally in both control and experimental groups. While DBP successfully induced new bone formation, the inability to adequately maintain the periodontal tissues due to bacterial accumulation in this model combined with recurrent pocket formation, precluded any conclusion regarding long-term advantage. Based on these findings, clinical trials of this or similar materials are recommended.