The clin. application of calcium phosphate ceramics as block material demands for definition and determination of mech. properties. The aim of this study was to characterize the mech. behavior of porous hydroxyapatite cylinders and to evaluate the influence of sterilization and storage on their compressive strength. Cylinders with a porosity of 60% and with 14 mm in diameter and length each were axially loaded to failure after sintering, after sterilization in the autoclave, and after storage under simulated in vivo conditions for 1, 3, 6 and 12 mo. The material behavior of the cylinders was brittle. The original reduced by more than 10% and 30% after sterilization and storage for 6 mo resp. This decrease in compressive strength for these two steps was significant.