The capacity of various pregnanes for counteracting androgen-induced defeminization was evaluated in an attempt to define some cellular mechanisms involved in the defeminization process. 5-day-old female rats received 60 µg testosterone propionate (TP) along with one of various pregnanes:progesterone, 5β-pregnandione, 5β,3α-pregnanolone, 5β,3β-pregnanolone, 5α-pregnandione, 5α,3β-pregnanolone, 5α,3α-pregnanolone or chlormadinone acetate. Protection against defeminization was defined as a significantly smaller proportion of anovulatory animals in a group compared to the control TP group. Data were analyzed at 60, 90 and 120 days of age. The anesthetic potency of the pregnanes was evaluated in 5-day-old male rats through the analysis of EEG and EMG records. Anesthetic pregnanes – progesterone, 5β-pregnandione and 5β,3α-pregnanolone – counteracted defeminization while nonanesthetic pregnanes – 5α-pregnanes, chlormadinone acetate and 5β,3β-pregnanolone – did not. The results show a clear relation between anesthetic capacity and protectio