In the present report the effects of postnatal (on day 1 after birth) male castration and female androgenization on vomeronasal organ (VO) development were studied. Control males showed greater values than females in VO volume and neurosensorial epithelium, while the opposite was true with respect to nuclear size. Postnatal treatments abolished these differences. It is suggested that the VO development is influenced by sexual hormones during at least a postnatal period as it occurs for several structures of the central nervous system connected with the VO.