Using immunoperoxidase labeling, we studied the subunit composition of nicotinic acetylcholine receptors, nAChR, in preparations of the inferior mesenteric ganglion, IMG, of the guinea pig. Antibodies against synthetic peptides corresponding to agonist-binding membrane components of the α3, α4, α5, and α7 nAChR subunits were used. The presence of α3-specific antibodies was revealed on the membranes of about 58% of large neurons and of all small ganglionic cells (means of the greater and smaller diameters of the somata 53.8 ± 1.8 vs 33.6 ± 1.4 μm, n = 20, and 14.1 ± 0.5 vs 7.5 ± 0.4 μm, n = 50, respectively). Labeled cells of the rostral node were distributed evenly, while those of the caudal node were localized mostly within the regions of branching of the lumbar, colonic, and both hypogastric tracts. Immune labels to the α4 subunit were observed only on the membranes of small ganglionic cells distributed mostly in the region of the internodal commissural tracts. α5-Specific labeling was found on the membranes of about 63% large neurons, whose distribution was similar to that of the α3-labeled units, and on all small cells. Immunoreactivity to the α7 subunit was observed only on the membranes of small cells concentrated around unlabeled large neurons in the region of branching of the intermesenteric, colonic, and both hypogastric tracts. Thus, nAChR in the guinea pig IMG include α3, α4, α5, and α7 subunits. The nAChR with α3 and α5 subunits are localized on the membranes of large ganglionic neurons, whose number and topographical distribution are very close to each other. Our data agree with our results of earlier electrophysiological experiments and are indicative of the crucial role of the α3- and α5-containing nAChR in synaptic transmission via the ganglion under study. The presence of the α4- and α7-containing nAChR was found only on small ganglionic cells (which are, probably, not the relay units) and their processes.