Abstract The localization of fibroblast growth factor receptor-1 was investigated in rat brain by immunohistochemistry using a polyclonal antibody against an acidic peptide sequence of chicken fibroblast growth factor receptor-1. For raising the antisera in rabbits, we synthesized the oligopeptide EDDDDEDDSSSEEKEAD which is a highly acidic region of chicken fibroblast growth factor receptor-1. The oligopeptide was used as a haptenic antigen by conjugating with poly- l-glutamate as a carrier protein. On immunospot assay, the best antiserum was capable of detecting 15.7 pmols of both the chicken and its analogous human oligopeptides but failed to react even with up to 1 nmol of poly- l-glutamate. When rat brain homogenate was examined by Western blots, the antiserum revealed two bands with molecular weights of 145,000 and 75,000 corresponding to known sizes of the membrane-bound and secreted forms of the rat receptor, respectively. Immunohistochemistry in rat brain demonstrated that putative fibroblast growth factor receptor-1 immunoreactivity sites were present mainly in neurons but also in tanycytes and ependymal cells. Positive neurons were distributed widely in various brain regions, but were particularly abundant in such regions as the lateral hypothalamus, substantia nigra, locus coeruleus and raphe nuclei. The present study suggests that fibroblast growth factor receptor-1 is expressed preferentially in certain neuronal systems that appear to be under the influence of fibroblast growth factors in the normal brain. The result should facilitate study of the functional significance of fibroblast growth factors in these brain neurons.