17β-Estradiol (E₂) was dissolved in the drinking water of female C57BL/6J mice and presented ad libitum. The oral administration of E₂ produced expected responses in E₂-sensitive target tissues. Vaginal smear cytology changed from the thin leukocytic smears characteristic of ovariectomized controls to thicker smears containing only cornified epithelial cells. Uterine weight and the specific activities of uterine glucose-6-phosphate dehydrogenase and alkaline phosphatase were elevated, while the postovariectomy elevation in serum luteinizing hormone (LH) was suppressed. However, oral E₂ did not influence the specific activity of uterine acid phosphatase.

During oral administration of E₂ through the drinking water, serum estrone and E₂ were elevated during the night and returned to low baseline levels during the day, in parallel with the circadian patterns of drinking. Similar transient elevations of serum E₂ levels were observed after subcutaneous injections of E₂. The oral administration of E₂ has advantages over the widely utilized parenteral routes of E₂ administration (i.e., injection or surgical implantation of E₂-containing capsules), particularly for long-term experiments, and may be more analogous to the usual oral route of estrogen administration in women as contraceptives or as postmeno-pausal estrogen-replacement therapy.