Osteoporosis is a prevalent disease in aging humans which results in a net loss of skeletal tissue. Since there is no satisfactory therapeutic treatment for osteoporosis, it is important to increase our understanding of the complex etiology of the disease with the aim of preventing its occurrence. Experiments are planned to investigate the effects and interaction of diet and physical exercise on the development of senile osteoporosis in animals. Studies will be carried out to elucidate the effect of the intake of dietary phosphate and calcium and the calcium:phosphate ratio on the development of osteoporosis in aging mice subjected to forced exercise. Studies will also be conducted to evaluate the interaction of high phosphate and titratable acid ash in the diet.