Removal of the vomeronasal organ eliminated androgen surges in male hamsters in response to female vaginal secretions in both sexually experienced and sexually naive males; lesions of the olfactory mucosa had no effect on such responses. Both lesions led to deficits in behavioral responses to vaginal secretions. In response to interactions with estrous females, in contrast, lesions of either system alone had no influence on androgen surges in males (either sexually experienced or naive). Lesions of both systems, however, eliminated androgen surges in sexually naive males but not sexually experienced males. These dual lesions eliminated male mating behavior, while lesions of either system alone had little influence on mating. There were no significant correlations in any experiment between level of behavioral responses and degree of change in androgen levels. Thus, we conclude that the vomeronasal system mediates androgen surges in response to female odors but is not necessary for such responses to females themselves. In sexually naive males the vomeronasal and olfactory systems together are necessary for androgen responses to females. Behavioral responses were influenced by lesions and by sexual experience. Lesions of both systems increased the latency to investigate vaginal secretions, and sexual experience decreased the latency and increased the duration of investigation. Lesions and experience also influenced male sexual performance.