PLAP is a tissue specific, trophoblast-derived, 70kDa, glycosyl-phosphatidylinositol (GPI)-anchored, dimeric, Zn2+ metallo glycoprotein that catalyzes the hydrolysis of phosphomonoesters into an inorganic phosphate and an alcohol. It is present in the placenta and serum of pregnant women and in high frequency in gynecological and testicular cancers and in lower frequency in other tumors. The three tissue-specific AP's in humans, PLAP, germ cell AP (GCAP) and intestinal AP, are 90-98% homologous. Non-tissue specific AP is found in kidney, liver and bone. This MAb binds equally well to all common allelic variants (S, F, FS and I) of PLAP as to AP from normal human testis. This MAb can be used both as coating as well as tracer antibody in the same ELISA to detect PLAP in serum of S, F, FS and I phenotypes.