A number of hormones are known to influence reproductive behavior in teleosts. The best studied in this regard are the sex steroids estradiol and testosterone. Sufficient evidence is available to permit the outlining of possible modes of action of these hormones on mechanisms controlling reproductive responses in fishes. Autoradiographic studies using tritium-labeled steroids have revealed several brain areas with neurons that concentrate testosterone and estradiol in both males and females. An area near the anterior commissure (preoptic region and parts of the area ventralis telencephali) is of primary interest for behavioral systems. Electrophysiological experiments in goldfish (Carassius auratus) have demonstrated that both hormones strongly influence olfactory mechanisms. These effects may be mediated by steroid feedback on brain areas involved in centrifugal control of the olfactory bulbs. The neurological substrates for several behaviors which are thought to be androgen dependent have been studied using classical neurobehavioral methods. These include: spawning and sperm release in goldfish and sunfish (Lepomis sp.) and courtship and nestbuilding in sunfish. As of yet, a direct action of sex steroids on these systems has not been demonstrated; however, they all relate to the steroid-concentrating area mentioned above. Some of the systems are incorporated into a tentative model of the neural–hormonal mechanisms controlling reproductive behavior in male goldfish.Key words: reproductive behavior, fishes, brain, hormones, sex steroids, olfaction