A model system of the irradiated rat mandible has been developed and used in conjunction with a non-spontaneously healing mandibular defect. The contribution of the tissue components in the healing of bony defects was studied using demineralized bone powder (DBP) prepared from unirradiated or in vivo irradiated rat long bones. Better bony fill of the defects occurred in the irradiated beds filled with unirradiated DBP than in the unirradiated beds containing irradiated DBP. This suggests that, at least in the early postirradiation period, the bed is not the limiting factor in healing of bony defects and the osteogenic components of bone in the DBP may be most affected by irradiation. In the irradiated bed, the defects grafted 2 weeks after irradiation healed better than those grafted at 4 weeks. Thus, the timing of surgery after irradiation also plays a role in the healing process, with early surgery producing better results.