Femurs of Sprague-Dawley rats were subjected to in vitro 3-Mrad irradiation and/or freeze-drying to investigate whether these processes have an order-dependent effect on the biomechanical properties of bone. Four experimental groups were designated-irradiated (RAD); freeze-dried (FD); irradiated, then freeze-dried (RAD/FD); and freeze-dried, then irradiated (FD/RAD). After the various treatments, the bones were inspected for microfractures and then torsion-tested. Microfractures were seen in more than 90% of the specimens that had undergone freeze-drying alone or with irradiation. Regarding the normalized relative ratios of torque, there was a statistically significant difference (P < .05) between the RAD group (1.0) and the 3 other groups (FD, .32; RAD/FD, .40; FD/RAD, .14). Differences among the FD, RAD/FD, and FD/RAD groups were not significant. However, a trend was bones were weaker than FD and noted: FD/RAD RAD/FD bones.