LRF producing neurons have been demonstrated in the Cebidae by the use of an antiserum against unconjugated synthetic LRF. These neurons are mainly localized in the medio basal hypothalamus and in the terminal lamina. Their axons form two different tracts, the first ending around the capillaries of the primary portal plexus and the second at the level of the vascular organ of terminal lamina and of its ependyma.