Visceral afferent neurons of the nodose and petrosal ganglia are immunoreactive (ir) for many neurotransmitters [e.g., substance P (SP), neurokinin A (NKA), calcitonin gene-related peptide (CGRP), and dopamine (tyrosine hydroxylase-ir; TH)]. Coexistence of SP-ir with NKA-, CGRP-, or TH-ir was studied in individual neurons of the rat ganglia using fluorescence immunocytochemistry. SP- and NKA-ir were present in equal numbers of cells and were consistently colocalized. SP- and CGRP-ir were found to be similarly distributed in scattered cells, concentrated mostly in the rostral pole of the nodose ganglion and in the petrosal ganglion. SP-ir completely coexisted with CGRP-ir. However, there was at least twice the number of CGRP-ir neurons as SP-ir neurons, and thus CGRP-ir neurons that did not contain SP-ir were also present. In contrast, SP- and TH-ir had different distributions in both the nodose and the petrosal ganglia. SP-ir was located in the more rostral regions of both the nodose and petrosal ganglia, whereas TH-ir was detected throughout the entire nodose ganglion and only in the most caudal region of the petrosal ganglion. There was no coexistence of SP- and TH-ir. These data demonstrate the differential localization and coexistence of putative transmitters in visceral sensory neurons in the nodose and petrosal ganglia.