Human chorionic gonadotropin hCG and fetal methylglobulin AFP are common germ cell tumor markers that can be used as indicators for diagnosis and activity determination. Germ cell tumors include germ cell tumors and non-germ cell tumors of germ cells. More than half of germ cell tumors express positive for human chorionic gonadotropin hCG and negative for fetal methylglobulin AFP. If the level of AFP increases in serum or cerebrospinal fluid, it indicates that the tumor is transformed to embryonal carcinoma. Non-germ cell tumors of germ cells include embryonal carcinoma, endodermal sinus tumor, choriocarcinoma and teratoma. Increased serum AFP level can diagnose non-germ cell tumor, increased hCG and AFP should be considered as embryonal carcinoma or mixed germ cell tumor, and elevated AFP significantly suggests possible endodermal sinus tumor. Besides, moderate elevation of blood hCG suggests possible germ cell tumor with syncytiotrophoblast giant cells, and if blood hCG is significantly elevated, choriocarcinoma or mixed germ cell tumor with choriocarcinoma component is considered. Prompt medical consultation is recommended when germ cell tumors are suspected, or when the above indicators are abnormal.