ABSTRACT In order to evaluate the usefulness of urinary sediment and buccal mucosal smears in comparison to vaginal smears for the assessment of estrogen effect, epithelial cell counts to determine the percentage of cornification were made daily throughout the menstrual cycle in 5 young women. The percentage of cornified cells found in the urinary sediment smears paralleled that found in the vaginal smears at various phases of the menstrual cycle, whereas the correspondence between vaginal and buccal smears was poor. The presence of estrogen-sensitive cells in the urinary tract was confirmed by study of a young woman with congenital absence of the uterus and vagina but with a known active ovary. In this subject, peaks of cornification were observed in the cells of the urinary sediment in regular association with the mid-cycle shift in basal body temperature. In cases in which vaginal smears are difficult to obtain, urinary sediment is satisfactory for cornification counts.