The paper deals with the design of a test arrangement capable of applying different combinations of static and fluctuating loads to the tibia of live rats. The Cyclic Loads are applied to the right tibia while the left tibia is constrained without subjection to external loads for comparison. Long duration tests at relatively low loads were performed to investigate the influence of cyclic stress on the physical characteristics and mineral content. Destructive, fatigue-type tests were also performed. Highly reproducible fracture data, and endurance limit are obtained.