The goals of this program relate to biochemical and endocrinological studies of calcified tissues and calcium homeostasis in the animal including investigations of the tissues themselves and of the mode of action, metabolism and biosynthesis of factors affecting calcified tissues and calcium homeostasis. Specific studies now in progress as phases of the overall program include a) Biosynthesis in vitro of parathyroid hormone (PTH), b) Action of vitamin D and PTH on calcium binding protein and intestinal transport of Ca, and c) Metabolic pathways in bone with emphasis on citrate metabolism.