Opossum pouch young, indifferent as to sex at birth, show stimulated responses of both sex ducts from treatment with ointments or injections of androgens or estrogens; duct inhibitions are not evident. Responses are revealed by day 16. Androgenic stimulation of Müllerian, and estrogenic stimulation of Wolffian, ducts are unexpected; female prostate induction occurs with androgenic treatment and male prostate inhibition with estrogenic treatment. Responses differ from those revealed in the free-martin.