The distribution of galanin was investigated at the light microscopic level in the human distal colon using immunocytochemical techniques. Galanin-like immunoreactivity was seen in nerve cell bodies in ganglia of the myenteric and submucous plexuses and in nerve fibres innervating all the muscle layers of the colon, the lamina propria, and epithelial cells at the base of crypts or lining the colonic lumen. Immunoreactivity was more intense in the circular muscle than in the longitudinal muscle or the muscularis mucosae. Immunoreactive nerve cell bodies were much scarcer in the myenteric than in the submucous plexus. Within subdivisions of the submucous plexus, galanin-like immunoreactivity was heterogeneously distributed. In Henle's plexus and Meissner's plexus 82-83% of galanin-positive cell bodies were up to 360 microns 2 in profile-area, but in the intermediate plexus nearly all (99.8%) were below 360 microns 2. The frequency-distribution of cell body area of galanin-containing nerve cell bodies was similar for Henle's plexus and Meissner's plexus but these two plexuses contain different size-populations of neurons when stained for NADH-diaphorase activity. Galanin-like immunoreactive nerve fibres were found in the plexus entericus (submucosus) extremus, and this is the first report of neuropeptide in this location.