OBJECTIVE Few studies have directly compared the quality of bone generated by distraction osteogenesis with that generated by autogenous onlay grafting. The purpose of this study was to compare rates of bone turnover at 5 months in bone produced by distraction osteogenesis and onlay grafting. METHODS Alveolar defects created in jaws of American foxhounds were augmented with distraction osteogenesis or onlay grafting and allowed to heal for 5 months. The animals were then sacrificed and the jaws were resected and prepared for decalcified and undecalcified histologic examination. RESULTS Both procedures produced bone containing a mixture of haversian systems and trabecular bone. A significantly greater ratio of osteoblast-covered bone surface to total trabecular bone surface (mean +/- SEM) was noted in distraction bone (0.124 +/- 0.049) compared to onlay bone (0.081 +/- 0.048) or control host bone (0.085 +/- 0.042 microm) (P < .05). In addition, significantly (P <.05) greater numbers of osteoclasts per microm of bone surface were noted in distraction bone (0.939 +/- 0.07) compared to onlay bone (0.605 +/- 0.06) or control host bone (0.725 +/- 0.08). No differences in rates of mineralization were noted between the groups. CONCLUSIONS While bone from both experimental groups appeared adequate for implant placement, distraction bone appeared to be remodeling at a higher rate than either onlay or control bone. CONCLUSIONS Given that the state of healing of the bone in each of these comparative groups was examined at a static point in time, it is premature to draw conclusions about the efficacy of one procedure over the other.