Parathyroid hormone and calcitonin are involved in the regulation of calcium metabolism via specific receptors in target organs principally bone and kidney. The pertinent findings in this rapidly evolving area of research are briefly summarized. The receptors for these two hormones have been extensively localised, the transduction of their signal studied, the structure and the proteins composing the receptors characterised by covalent linking and purified by affinity chromatography or specific immunoprecipitation. The sequence of the receptors will be established in a near future using genetic engineering.