Estrogen receptor localization in normal and neoplastic epithelium of the uterine cervix. To investigate the estrogen receptor (ER) status of cells during carcinogenesis of the uterine cervix, the immunohistochemical reactivity for a monoclonal anti-ER antibody (H 222) was studied in 26 normal cervical specimens, 21 cases of cervical intraepithelial neoplasia (CIN), and 21 cases of invasive cervical carcinoma. In addition, the presence of human papillomavirus (HPV) DNA (types 6/11, 16/18, or 31/33/35) was analyzed by in situ hybridization. In the normal cervix, basal cells of the squamous epithelium, metaplastic cells, and endocervical glandular cells were ER positive. In contrast, neoplastic cells of CIN (17 of 21 cases) and invasive carcinoma (19 of 21 cases) were ER negative. The remaining four cases of CIN and two cases of invasive carcinoma were focally ER positive. The HPV DNA analysis revealed that HPV DNA in ER-negative cases was either types 16/18 or undetectable, but all ER-positive neoplasms contained HPV DNA types 31/33/35. These results suggest that most neoplastic cells in CIN and invasive cervical carcinoma lose their ER expression and that this may be related to the HPV DNA types which they possess. 