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 (AFP) is synthesized by the cells of the embryonic yolk sac, fetal liver and fetal intestinal tract. This secretory protein is synthesized primarily in the fetal liver whereas expression is repressed in adult liver. Anti-AFP has been immunohistochemically demonstrated in hepatocellular carcinoma (HCC) and shows no immunoreactivity in normal liver. 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 tumor. The anti-AFP antibody may be useful for the identification of neoplastic liver diseases, yolk sac tumors and mixed germ cell tumors.