37 cases of yolk sac tumor were treated in our hospital from 1966-1989. Serum AFP were measured. The diagnosis of yolk sac tumor was confirmed by light microscope

10 cases were further examined with electron microscope and 8 cases with AFP immunohistochemistry study. Related literature reviewed. These studies confirm the concept suggested by Telium. i. e. histogenesis of the tumor arising from germ cell differentiating along dorsal wall of yolk sac.1. AFP had been synthesized in yolk sac of embryo. On our study AFP elevated predominately and had been localized by immunoenzymatic labelling PAP methods.2. Electron microscope examination showed that morphology of this tumor is similar with normal human yolk sac at 7 weeks gestation and those finding demonstrated epithilial and mesothelial element is the same as the extia-embryonic endoderm and mesoderm.The terminology of this tumor

the associated relation with teratoma and practice of immunohistochemistry have been discussed