Selenoprotein-P (SelP) is the major selenoprotein in human blood plasma and a transport protein which is carrying selenium to various extrahepatic tissues. Though its expression is detected in most tissues, highest amounts are produced by the liver, which secretes highly glycosylated SelP into plasma. Purification of human SelP yields two distinct isoforms with 61 and 55 kDa, differing in selenium content. SelP also has been shown to chelate heavy metals such as cadmium and mercury, and there are several evidences about its serum antioxidant capacity and protection against oxidative stress. Selenium deficiency predispose to several pathological condition such as cancer, coronary heart disease and liver necrosis although the biological function of SelP in various pathologic conditions has not been established. Might be responsible for some of the extracellular antioxidant defense properties of selenium or might be involved in the transport of selenium. May supply selenium to tissues such as brain and testis.