Abdominal vagal afferent fibers were selectively labeled by injecting the fluorescent carbocyanine dye DiI into the left nodose ganglion of rats. Almost all paraganglia that were distributed along the five major abdominal vagal branches and their subbranches were found to be innervated by labeled vagal afferents. Laser scanning confocal microscopy with its single optical sectioning and three-dimensional reconstruction capabilities were used to analyze this innervation in more detail for paraganglia near the vagal hepatic branch and liver hilus. Furthermore, in double-labeling studies, it was demonstrated that a large percentage of the vagally innervated glomus cells were capable of catecholamine synthesis on the basis of their positive staining for tyrosine hydroxylase antibody. These findings support the concept of a chemoreceptive function for the abdominal paraganglia.