Alpha-fetoprotein(AFP) is the most abundant plasma protein found in the human fetus. It is thought to be the fetal form of serum albumin. AFP binds to copper, nickel, fatty acids and bilirubin and is found in monomeric, dimeric, and trimeric forms. Alpha-fetoprotein is synthesized by the cells of the embryonic yolk sac, fetal liver and fetal intestinal tract. AFP levels decrease soon after birth. In abnormal tissues, expression of AFP has been demonstrated in hepatocellular carcinoma, hepatoid adenocarcinoma, germ cell tumors and particularly yolk sac tumors and mixed germ cell tumors. The anti-AFP antibody may be useful for the identification of neoplastic liver diseases, yolk sac tumors and mixed cell tumors.