While many, if not most, of the details remain to be worked out, bone cell function is increasingly being explained in terms of cell membrane phenomena. Ultrastructurally, bone cell membranes do not show remarkable features beyond those associated with the ruffled border and clear zone of the osteoclast or specializations associated with the formation of matrix vesicles. Major physiologic properties of bone cell membranes are related to calcium transport, electrical properties and hormonal responses. Major advances in these areas are occurring with the development of separation techniques for the isolation of subpopulations of bone cells that respond primarily to parathyroid hormone or calcitonin. The combined actions of calcium and cyclic AMP in large part mediate the hormonal and possible electrical responses of bone cells.