Placental Alkaline Phosphatase (PLAP) reacts with a membrane-bound isozyme (Regan and Nagao type) of PLAP occurring in the placenta during the 3rd trimester of gestation. This antibody is highly specific to PLAP and shows no cross-reaction with other isozymes of alkaline phosphatases. It is useful in the identification of testicular germ cell tumors and in separating thymic neoplasms from germ cell tumors. Unlike germ cell tumors, PLAP-positive somatic cell tumors uniformly express epithelial membrane antigen (EMA). PLAP may also be a useful marker in distinguishing classical seminoma from spermatocytic seminoma.