Neurones in the ureterovesical ganglion complex provide autonomic innervation to the pelvic ureter, the ureterovesical junction and the bladder trigone. We examined the distribution and peptide co-expression pattern of nitric oxide synthase (NOS) in the human ureterovesical ganglia by combining NADPH-diaphorase histochemistry with immunoreactivity for vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP). Less than 20% of nerve cells in the large ganglia of the ureterovesical complex were stained for NOS activity. In elderly individuals, ganglion cells regularly exhibited conspicuous morphological alterations suggestive of degenerative changes. Most of the NOS-positive cell bodies costained for VIP-immunoreactivity. A minority of NOS-expressing cells also reacted for NPY-immunoreactivity. CGRP-immunoreactivity was present in varicose terminal-like nerve fibres which were found to encircle NOS-containing perikarya. Occasionally, NOS-positive somata were surrounded by plexiform axon terminals which immunostained for VIP or NPY. We conclude that the passage of urine across the ureterovesical junction is under relaxatory control of a local nitric oxide/VIP(NPY) pathway which may be modulated by preganglionic efferent and/or primary afferent input.