The main goal of this study is to establish an animal model system which can be used to monitor age changes in bone activity which may relate to defects underlying osteoporosis and allow novel therapies to be tested. An injury model, involving bone marrow aspiration was used to induce rapid production of bone in the marrow cavity. This process can be quantitated by measuring the expression of genes involved in bone formation and resorption. This model was also used to examine the response of aged animals and indicated that bone induction was severely attenuated with age. Currently, we are using this model to evaluate the effectiveness of various novel interventions including growth factors, stem cells and gene therapy in restoring the ability of old animals to form bones.