In order to analyze Oncotrophoblast antigen, I used monoclonal antibodies (MoAbs) TM7-3 and TM3-8, which demonstrated a very strong reaction with choriocarcinoma, particularly cytotrophoblast-like tumor cells, in spite of a very weak reaction in normal chorionic villi. I examined their reaction with other tumors of non-trophoblastic origin. Those examined were 58 malignant cases, 2 low-potential malignant cases and 14 benign cases. Immunofluorescence and immunoperoxidase stainings show that 1) TM7-3 and TM3-8 had similar patterns of distribution. 2) In various normal tissues tested, only a part of the urinary tubules of the kidneys and the duct of the pancreas reacted with these MoAbs. 3) In various neoplastic tissues, ovarian serous cancer (3/6), ovarian clear cell cancer (3/3), ovarian undifferentiated cancer (2/2) and well differentiated uterine corpus cancer (3/3) showed a positive reaction with TM7-3 and TM3-8. On the other hand, no uterine cervical squamous cell cancer (0/20) showed a positive reaction. These results suggest that TM7-3 and TM3-8 may be valuable for research on the relationship between the oncotrophoblast antigen and adenocarcinoma of the ovary.