AbstractTo explore the changes in the relationship between skeletal and Ca2+homeostasis with age, we studied 50 dogs divided into four age groups. The skeletal uptake of85Sr decreased markedly with age, and the immunoreactive parathyroid hormone (iPTH) level increased. There was a significant correlation between iPTH value and the calculated short‐term exchange of Ca in bone (r = −0.55; p<0.001). Bone formation and bone resorption decreased with age except that in the oldest group of dogs the resorption increased (p<0.001). We suggest that in aging dogs the skeletal exchange of Ca falls to a very low level that decreases the immediate effect of PTH and thus leads to a chronic net increase in circulating PTH. Concomitant with this is an increase in osteoclastic bone resorption and, over a long time, loss of skeletal m