Cellular localization of amylase in 100 endometrial carcinomas was studied by the immunoperoxidase method using an antibody to human pancreatic amylase. Amylase activity was observed in 12 tumors, localizing in the cytoplasm of tumor cells. They were seven well-differentiated adenocarcinomas, one poorly differentiated adenocarcinoma, one papillary serous carcinoma, two mucinous carcinomas, and one adenocarcinoma with squamous differentiation. Of these, many amylase reactive cells were found in one well-differentiated adenocarcinoma, one papillary serous carcinoma, and one mucinous carcinoma. The remaining nine tumors contained a few to a moderate number of amylase reactive cells. Although serum levels of amylase were not examined in the present study, the results suggest that amylase may be a potential tumor marker for some endometrial carcinomas.