To investigate the role of brain-derived neurotrophic factor in the central nervous system, we produced an anti-peptide antibody that specifically recognized brain-derived neurotrophic factor and performed immunohistochemistry for brain-derived neurotrophic factor-like immunoreactivity in normal adult rat brain. A synthetic peptide (EKVPVSKGQL), derived from mature brain-derived neurotrophic factor, was conjugated to bovine thyroglobulin at a ratio of 1:3 and used as an immunogen to produce a high-titre anti-brain-derived neurotrophic factor polyclonal antibody in Japanese white rabbits. Dot blotting demonstrated that the antiserum could detect 3.91 pmol of synthetic peptide, and Western blotting showed that the antiserum recognized one band with a molecular weight consistent with that of brain-derived neurotrophic factor. In immunohistochemistry, brain-derived neurotrophic factor-like immunoreactivity was widespread in adult rat brain, including cerebral cortex, hippocampus, basal forebrain, striatum, hypothalamus, brainstem and cerebellum. Not only neuronal somata but also nerve fibres showed positive staining. Our data suggest that brain-derived neurotrophic factor is transported through axons in a subpopulation of neurons in adult rat brain, and that brain-derived neurotrophic factor influences a great variety of neurons and acts as a neurotrophic factor in the central nervous system.