Information concerning localization of exogenously administered tritiumlabeled steroid hormones in the brain by dry-mount autoradiography was presented. Estrogens, androgens, and glucocorticoids were found to be concentrated and retained in nuclei of certain neurons. The autoradiographic information on the topographic distribution of hormone-neurons (neurons which concentrate, retain, and respond in a specific manner to hormones) suggested that "feedback" areas for the regulation of endocrine glands are not restricted to the hypothalamus and preoptic region. It appeared that gonadotropin and neurons that regulate sexual behavior were widespread within the phylogenetically ancient periventricular brain, following the origin, the termination, and to some degree, the path of certain nerve-fiber tracts. In the case of estradiol and androgen, likely to be involved are the stria terminalis, the ventral amygdalohypothalamic pathway, a portion of the fornix, the periventricular bundle, and others. Hormone-neurons have been found only in the periventricular brain but not in the neopallium. It was concluded that the "hypophysiotropic area" is probably not restricted to a limited hypothetical segment of the hypothalamus but is identical with the multiple sites of autoradiographically defined hormone-neurons within the phylogenetically older periventricular brain.