Using the indirect immunofluorescence method, the distribution of galanin (GAL)- and galanin message-associated peptide (GMAP)-like immunoreactivities (LI) were studied in sympathetic ganglia and the adrenal gland of the guinea pig. A rather dense network of GAL-immunoreactive nerve fibers was found in the inferior mesenteric ganglion (IMG) and in the superior mesenteric pole of the celiac-superior mesenteric ganglion complex (C-SMG). The celiac pole of the C-SMG, the stellate ganglion, and the superior cervical ganglion contained fewer, mostly scattered fibers. SIF-cells in prevertebral and paravertebral ganglia contained GAL-LI, as did the adrenal medullary cells. The GAL fibers in the IMG surrounded mainly principal ganglion cells containing somatostatin-immunoreactivity (SOM-IR), whereas fewer fibers were seen around neuropeptide Y (NPY) cells and cells in which SOM and NPY coexisted. Application of colchicine or vinblastine onto the IMG did not result in the appearance of GAL-IR in the principal ganglion cells. In denervation experiments it was revealed that most of the GAL fibers reach the IMG via the lumbar splanchnic nerves. GAL-IR appears to be colocalized with substance P (SP) in fibers of the IMG, indicating an origin of the GAL-containing fibers in dorsal root ganglia (DRG). This conclusion was supported by the finding in lumbar DRGs of GAL-positive cell bodies that contained SP. The role of GAL in prevertebral ganglia is unclear. It may be suggested that GAL modulates the slow, long-lasting membrane depolarization of the principal ganglion cells caused by SP in the primary afferents related to the IMG. GMAP-LI was detected in SIF cells and adrenal medullary cells in which GMAP-LI parallels the immunoreactivity of GAL. GMAP-LI was not observed in neuronal cell bodies or nerve fibers of the ganglia.