Epidermal growth factor receptor expression in fresh-frozen uterine tissues was studied with the use of monoclonal antibody 528, which recognizes an epitope on the external domain of the epidermal growth factor receptor. Immunohistochemically detectable epidermal growth factor receptor was seen in all uterine cell types in 19 of 20 normal uteri. Staining of endometrial glands and endometrial stromal cells was consistently greater than that of myometrium, and no variation in intensity or distribution of staining was seen during the menstrual cycle. Immunohistochemically detectable epidermal growth factor receptor was found less frequently in endometrial adenocarcinomas than in normal endometrium (p less than 0.01). Thirteen of 40 endometrial adenocarcinomas (32.5%) did not express detectable receptor. Epidermal growth factor receptor expression did not correlate with histologic grade, depth of myometrial invasion, estrogen-progesterone receptor status, the presence of extrauterine metastases, or the development of recurrent disease.