It is evident that in the past decade much new information has been gathered regarding calcium metabolism at the physiological and extracellular level. In addition, new information is becoming available regarding intracellular mechanisms of calcium transport and mobilization. Finally, during the past decade the hormone calcitonin has been introduced as well as a hormone derived from vitamin D, namely 1,25-(OH)2D3, has been discovered and demonstrated to play a central role in the regulation of calcium metabolism. The exciting developments will undoubtedly foster the revelation of new information during the next decade which hopefully will bring about an elucidation of the molecular mechanisms of calcium metabolism.