Little data exist on the expression of epidermal growth factor receptors (EGF-Rs) in human endometrial cancer. EGF-R status was studied in 65 patients with endometrial carcinomas and in 26 women with nonmalignant postmenopausal endometria, either inactive/atrophic endometrium or adenomatous hyperplasia. EGF-R was identified on frozen tissue sections by means of an indirect immunoperoxidase technique with a monoclonal antibody against the external domain of the EGF-R. Seventy-one percent of the carcinomas expressed positive EGF-R immunoreactivity. In general, staining was most prominent at the cell membranes, with a varying pattern in individual carcinomas. EGF-R expression was not correlated with histologic grade, surgical stage, or estrogen/progesterone receptor status evaluated immunohistochemically or biochemically in adjacent tissue sections of the tumor. Ten of 13 (77%) atrophic/inactive endometria and seven of 13 (54%) endometria with adenomatous hyperplasia were EGF-R positive, with an immunostaining pattern rather similar to that of the carcinomas.