Parathyroid hormone is a circulating hormone that acts as the central regulator of calcium metabolism by directly targeting bone, kidney, and intestine. The classical concept of PTH action is that it regulates serum calcium levels by stimulating bone resorption. However, intermittent administration of PTH selectively stimulates bone formation. It is now known that PTH binds to its receptor PTH1R, and activates the G protein alpha subunits. Besides PKA and PKC activation, PTH also regulates MAPKs including p42/p44 ERKs, p38, and c-Jun N-terminal kinase subtypes.