This bone project is dedicated to the measurement of the intrinsic composition of bone through the use of a new non-invasive in vivo method. This method involves the measurement of the velocity of ultrasound in cortical bone, the measurement of the bone mineral content by a photon absorption technique (Cameron-Sorenson), and obtaining the cortical geometry from a single radiograph. The site of all measurements is the proximal radius. For the first time the elastic modulus of cortical bone can be measured in vivo. The accuracy and dependablity of this new method has already been established by parallel tests in vitro, aad by comparison of literature values. Data from normals and from a heterogenous group of patients, referred to an orthopedic clinic with assorted skeletal problems has already been obtained and this continues to be expanded. Data from patients with osteoporosis and with renal failure are now being obtained and analyzed. The importance of this work lies in the fact that there has been hitherto no acceptable in vivo method of diagnosing the generalized skeletal changes which occur in such conditions as osteoporosis and metabolic osteodystrophy before they are present as disabling fractures or bone pain. By the same token there has been no in vivo method hitherto of assessing the efficacy of any form of treatment. It is the aim of this project to provide such an index and the results so far lead us to believe that the project will succeed.