Immunofluorescence microscopic studies revealed a corticotropin-releasing factor (CRF) staining within both myenteric plexus perikarya and nerve fibres of the rat duodenum. A CRF-immunofluorescence could be visualized also within nerve fibres close associated with myenteric and submucous blood vessels. Even the lamina propria contained CRF-immunoreactive nerve fibres, which were obviously often localized near the basal lamina.