In the present study the regulatory action of the non-aromatic androgen dihydrotestoterone (DHT) on the volume of the sexually dimorphic bed nucleus of the accessory olfactory tract (BAOT) was investigated. Postnatal treatment with DHT (180 micrograms day-1) between days 6 and 20 (D6-D20) induced, in gonadally intact male rats, a drastic reduction in the overall volume to levels typical in control females. Conversely, the postnatal administration of the anti-androgen cyproterone acetate (CA) to the females from D6-D20 produced an increment in the BAOT volume not dissimilar to that found in control males. These findings reveal that sexual organization in this vomeronasal structure is dependent on the presence of DHT in females during postnatal development.