Nitric oxide (NO) is an intercellular messenger molecule in the nervous system and exerts its action in many regions by generating cyclic GMP (cGMP) via soluble guanylyl cyclase. In this study, on the male guinea pig, we have analyzed the localization of cGMP in some autonomic ganglia with immunohistochemistry after stimulation with sodium nitroprusside (SNP) as NO donor, and made correlations with the NO synthesizing enzyme NO synthase (NOS), tyrosine hydroxylase (TH) and some neuropeptides. The putative target neurons for NO were examined in the anterior pelvic ganglia (APGs), as well as some pre- and paravertebral sympathetic ganglia. The results show that cGMP-like immunoreactivity (LI) in the APG was in most cases observed in the TH-positive, NOS-negative neuron population after SNP stimulation, whereas the NOS-expressing cholinergic population mostly lacked detectable cGMP-LI. In the pre- and paravertebral ganglia, SNP stimulation increased cGMP levels to a much lesser extent than in the APGs. cGMP was also observed in blood vessels, in the ganglion capsule, and in some cases. possibly in satellite cells. We propose, as one alternative, that there is a functional, intraganglionic regulatory loop between the parasympathetic and sympathetic divisions of the APG, using the NO/cGMP pathway.