This report describes osteoclastic bone resorption around intraosseous fixation screws in rat and pig mandibles. These screws supported distraction devices and provided for neutral fixation following the distraction period. Progressive clinical instability of bicortical screws and radiographic and histologic evidence of osseous resorption were frequent findings. In rats, clinical evaluation revealed screw loss and/or loosening in 50% of the rats between 11 and 30 days of neutral fixation. Radiographic signs of resorption were apparent around 60% of the screws that were in place at the end of the observation period. The total rate of resorption or loss was 64 of 80 screws (80%). Histologic examination showed partial or extensive osteolysis around the screw holes in 87% of screws that were clinically fixed in the bone at sacrifice. In histologic sections of porcine specimens, osseous resorption around identifiable screw holes was present in 75% of the cases, and showed progressive increase in resorption with time. Osteoclastic resorption was common around bicortical screws that were evaluated after they had served for osseous stability.