l-Arginine is a precursor of nitric oxide that has been identified as an endogenous activator of soluble guanylate cyclase. We have recently reported the immunocytochemical localization of free l-arginine in glial cells in the central nervous system (CNS) using specific anti-arginine antibody. In the present study, we focused our attention on this particular amino acid in the peripheral nervous system (PNS). In the cochlea of the inner ear, arginine-like immunoreactivity was localized in satellite cells surrounding neurons of the spiral ganglion. In the dorsal root ganglia, satellite cells surrounding sensory neurons were found to be immunoreactive. In the superior cervical ganglion, l-arginine was concentrated in satellite cells around neuronal cells. In ganglia of the enteric plexus, supporting cells that covered neuronal cells were stained. These results show that free l-arginine in the PNS is concentrated in satellite and supporting cells, both of which correspond to glial cells in the CNS. Thus, those cells in ganglia of the PNS may support and/or control the neural activity by providing l-arginine to the neurons that they surround.