We present evidence that the polar, matrix-forming osteoblasts are connected laterally to form an impervious layer of cells. Next, the possible mechanisms by which calcium ions are translocated across the layer of cells into sites of mineralization are analyzed. Finally, mechanisms of attachment of bone-resorbing osteoclasts are considered. Osteoclasts adhere to matrix, in part, though an arginine-glycine-aspartic acid (RGD)-dependent mechanism. Adherence is under control of parathyroid hormone and 17β-estradiol.