Alkaline phosphatases are a heterogeneous group of glycoproteins confined to the cell membranes. There are three tissue-specific alkaline phosphatases; PLAP, germ cell AP (GCAP) and intestinal AP (IAP), which are 90-98% homologous with a molecular weight of 57-70 kDa. Since different antibodies may recognize PLAP alone, or PLAP together with the other AP’s and TNAP, the reaction pattern may be varying. However, in general, PLAP can be recognized consistently in seminoma/dysgerminoma/germinoma (with the exception of spermatocytic seminoma) and intratubular germ cell neoplasia (carcinoma in situ testis) as well as in most cases of embryonal carcinoma and some cases of yolk sac tumour. Hydatiform mole and choriocarcinoma are also PLAP positive. PLAP is an important marker in the identification of germ cell tumours and intratubular germ cell neoplasia. However, OCT3/4 appears to show a higher signal/noise ratio. Also PLAP has been used in the differential diagnosis of uncharacteristic tumours in, e.g., mediastinum. PLAP may also be used in the panel for the recognition of unusual neoplasms such as desmoplastic small round cell tumour, rhabdomyosarcoma and choriocarcinoma. Placenta is the best choice regarding positive control, in which the cytotrophoblasts and syncytiotrophoblasts must show an as strong as possible predominantly membranous but also cytoplasmic staining reaction, while no staining should be seen in the stromal cells. Appendix may be used as negative control, in which no structures/cells should show any staining reaction.