Fourty-six cases of gestational trophoblastic neoplasms (32 cases of hydatidiform mole; 4 cases of invasive mole; 10 cases of choriocarcinoma) and five cases of normal pregnancy as control group were studied for the distribution and intensity of human chorionic gonadotropin(HCG), human placental lactogen(HPL) and regnancy specific beta-1 glycoprotein(SP-1) by immunoperoxidase method. The following results were obtained. 1) The HGC was seen in the syncytiotropholasts, but not cytotrophoblasts of normal placental tissue and hydatidiform mole in all 3 grades. However, in the invasive mole and choriocarcinoma, the HCG was also seen in the cytotrophoblasts. 2) The HPL and SP-1 were only seen in the syncytiotrophoblasts in all those trophoblastic neoplasms. 3) The more malignancy was progressed, the more intensity of the HCG in the syncytiotrophoblasts was increase. Especially, it was severe intensity of positivity in the choriocarcinoma. 4) Intensity of the HPL in the syncytiotrophoblast had the tendency of increase in the invasive mole. But, it was variable in the choriocarcinoma. 5) Intensity of the SP-1 in the syncytiotrophoblast had the tendency of increase in the grade II of hydatidiform mole. But thereafter, it was decreased or variable in more aggressive trophoblastic neoplasms, In conclusion, the HCG, HPL and SP-1 were present in the syncytiotrophoblasts of normal placental tissue and various trophoblastic neoplasms. And, the more severe hyperplasia and undifferentiation of trophoblasts were seen, the more intensity of the HCG was increased, suggesting that the HCG can be a useful tumor marker of prognosis in gestational trophpblastic neoplasms.