Estrogen receptors (ERs), progesterone receptors (PRs), and P29, an ER-associated protein, were studied immunohistochemically in human cervix with use of specific monoclonal antibodies. In ectocervical epithelium, homogeneous staining was found for P29 throughout the menstrual cycle and after menopause. Weak or moderate staining was found for ER in the basal and, occasionally, the parabasal layers of ectocervix during the proliferative phase. In contrast, staining decreased in secretory phase and postmenopausal epithelia. Staining was negative for PR in all the exocervical epithelia. Heterogeneous staining, more pronounced for P29, was found for the three antigens of the study in endocervical epithelium. Staining did not change with the hormonal status of patients, except for ER, where staining decreased during the secretory phase. Stromal cells were negative or weakly positive, whereas muscular fibers were positive. This study suggests that the capacity of response of the steroid apparatus of cervical cells to fluctuations of circulating estrogens and progestins is limited compared with some of the cell functions, such as mucus secretion, or with other target tissues, such as endometrium. Additionally, the differences found in the pattern of expression of the three antigens studied suggest that the steroid-dependent growth and differentiation in ectocervix is regulated differently to endocervix.