Bone sialoprotein (BSP) is one of the major noncollagenous proteins in the extracellular matrix of bone. It is a phosphorylated glycoprotein with an approximate molecular weight of 70-80kD. The protein has been found in osteoblasts and osteocytes. BSP is synthesized and secreted by bone-, dentin- and cementum-forming cells. Diseases concerning the bone turnover, pathological bone alterations as well as the rapid increase of osteoporosis make it necessary to establish new markers. Bone sialoprotein is discussed as a potential serum marker for monitoring bone remodelling.