Atresiaor stricture of the orifice of vagina was detected in 100% of female Sprague-Dawley rats injected subcutaneously within 24 hours after birth with testosterone propionate (lmg), 5a-dihydrotestosterone (lmg) or 5a-androstane-3a, 17S-diol (lmg) but was not found in any neonatally intact female rats.On the contrary, a single injection of estra-1, 3, 5(10)-triene-3, 17jS-diol (iOog) in female rats had no effects.When 5a-dihydrotestosterone (lmg) was given into female rats at 0, 1, 2, 3 or 5 days of age, the incidences of the atresia were 85.7%, 63.6 %, 25.0%, 0% and 0%, respectively.