We tried to understand how hypophysiotropic polypeptides could be carried into some areas of the central nervous system. Granulations of neurosecretion in the ependymal cells and the presence of releasing hormones in the cerebrospinal fluid (CSF) suggest that CSF may transport these substances between the hypothalamus and other areas in the brain. Direct connections between the hypothalamus and other parts of the brain through secreting neurons are not necessary, the CSF transmitting to the cerebral hemispheres the hypothalamic polypeptides by the ventricles at the infundibulum.