Abstract
Through the use of immunohistochemical techniques, human chorionic gonadotropin has been localized to syncytiotrophoblastic cells of immature placenta, hydatidiform mole, chorioadenoma destruens, and choriocarcinoma. No gonadotropin has been detected in cytotrophoblast. Evidence is discussed which suggests that syncytiotrophoblast is the cell of origin of human chorionic gonadotropin. The observation that formalin fixation did not alter the ability of human chorionic gonadotropin to react with its specific antibody permitted the study of formalin-fixed paraffin-embedded tissues stored in the tissue collection. In addition, the excellence of histologic preparations following formalin fixation facilitated cytologic identification.