Several studies demonstrated the necessity of rehydration of lyophilized bone allografts prior to implantation. The purpose of the presented study was to evaluate the influence of different rehydration periods on the stability of human cortical lyophilized and gamma-irradiated allografts, the capability of lyophilized bone for rehydration, as well as the effects of lipid extraction on rehydration. Breaking strength of lyophilized irradiated cortical bone after different rehydration periods (0.5, 1, 2, 4, 8 hours) showed no significant difference. Weight reduction after lyophilization of human femoral heads was between 7.6% and 41%. Further weight reduction occurred after lipid extraction (38.7%). Total weight loss was 56.9%. There was a significant influence of intraosseous lipid content on the rehydration capability. After lyophilization alone the rehydration weight after 8 hours was only 18.1%, whereas after lipid extraction the weight increase was 43% after 0.5 hours, 36.4% after 1 hour, 57.6% after 2 hours, 60% after 4 hours, and 92.7% after 8 hours. CONCLUSIONS Based on the presented data rehydration time of 0.5 hours seems to have no disadvantage compared to longer time periods concerning breaking strength. Therefore a longer intraoperative time period seems not to be necessary. This is of advantage for a possible secondary contamination while the allograft is rehydrated. Rehydration after lipid extraction is more effective than rehydration after lyophilization alone. However, the question whether lipid extraction alter bone stability has to be proved in further studies.