Female mice of the C57 Black/Tw strain were injected daily with 100 microgram testosterone, 50 microgram testosterone propionate (TP), 100 microgram 5alpha-dihydrotestosterone (DHT) or 50 microgram 5alpha-dihydrotestosterone propionate (DHTP), for 10 days from the day of birth. Two other groups of female mice were given neonatal injections with 20 microgram estradiol-17beta and 100 microgram progesterone for 10 days, respectively. All mice were ovariectomized at 60 days of age and killed at 90 days. In 100% of neonatally estrogenized or androgenized, ovariectomized mice, the cranial part of the vagina was lined with stratified epithelium with either cornification or parakeratosis or mucification. Stratification only or stratification with superficial squamous metaplasia or cornification took place in the uterine epithelia of 18% of the TP-treated, 75% of the DHT-treated and 50% of the DHTP-treated, ovariectomized mice. In contrast, neonatally estrogenized, ovariectomized mice did not show the estrogen-independent, persistent uterine changes. Neonatal progesterone treatment failed to induce the permanent changes in the vaginal and uterine epithelia.