This study was designed to further elucidate an estrone-parathyroid extract antagonism in bone. The incorporation of acetate-1-C14 into bone citrate was measured in the presence of both substances administered singly and in combination. Estrone increased bone citrate synthesis and concentration while parathyroid extract enhanced labeled citrate formation with little change in bone citrate concentration. When both materials were administered the results were essentially those observed for estrone alone although the changes were not as great.