Vomeronasal chemoreceptors segregated within the vomeronasal organ are important for male hamster sexual behavior. An autonomically controlled vascular pump, previously demonstrated in anesthetized animals, can transport stimuli to the receptors. Interruption of the efferent nerves controlling the pump results in behavioral deficits similar to those produced by interruption of the afferent nerves carrying information from the vomeronasal organ to the brain. Pump activation is thus a prerequisite for normal vomeronasal stimulation in behaving animals.