Fetuin, a glycoprotein present in the circulation, is synthesized by hepatocytes. The fetuin molecule consists of two polypeptide chains, which are both cleaved from a proprotein encoded from a single mRNA. The protein is commonly present in the cortical plate of the immature cerebral cortex and bone marrow hemopoietic matrix. Its function of inhibiting soft tissue calcification is achieved by forming a soluble colloidal microsphere of fetuin-calcium-phosphate complex in the blood stream. It has the highest capacity in inhibiting soft tissue calcification among all other molecules in the circulation. It is the most important and major calcification regulating protein in the circulation.