Alkaline phosphatases (ALP) are dimeric enzymes by glycosylphosphatidylinositol anchors to the cell membrane. There are at least four distinct but related isozymes: placenta ALP (PLAP), germ cell ALP (PLAP-like or GCAP), intestinal ALP (IAP) and non-specific tissue ALP (TNAP). These isozymes may serve to guide migratory cells, to transport specific molecules such as fat and immunoglobulins across membranes or to detoxify lipopolysaccharide and prevent bacterial invasion across the gut mucosal barrier. This antibody specifically recognizes PLAP and GCAP. PLAP is expressed in the human placenta beginning late in the first trimester of pregnancy. GCAP is expressed in normal endocervix and fallopian tube. Ectopic expression of GCAP is associated with germ cell tumors: intratubular germ cell neoplasia, unclassified (IGCNU), seminoma, embryonal carcinoma and choriocarcinoma. PLAP has been used as a marker for germ cell tumor. Clinically, it is useful for the identification of primary intracranial germinoma.