A fluorescent antibody study of LRF-producing neurons was made with antisera to synthetic LRF in normal male and female cats and dogs. Specific immunoreactive perikarya have been found in the rostral hypothalamus of both species. In the dog, specific immunoreactive perikarya have also been found in the pars oral¡s tuberi, the infundibular nucleus, the premammillary region, and even the dorsomedial and ventromedial areas and the rostral mesencephalon