The distribution and frequency of NO synthase (NOS)-immunoreactive (IR) nerves in relation to the general autonomic innervation, adrenergic, cholinergic and some peptidergic nerves, were investigated in the female rat urinary tract. NOS nerves were very frequent in the smooth musculature of the urethra together with cholinergic, adrenergic and neuropeptide Y (NPY)-IR nerves, whereas vasoactive intestinal peptide (VIP)-IR and calcitonin-gene-related peptide (CGRP)-IR nerves were much less abundant. NOS-IR, CGRP-IR and cholinergic nerves were also frequent in the longitudinal smooth musculature of the distal ureters and the ureteral orifices into the bladder, where no adrenergic, NPY-IR and VIP-IR nerves were found. In contrast, in the detrusor NOS-IR nerves were scarce. Bilateral pelvic ganglionectomy very pronouncedly decreased the number of any of the populations of nerves studied, whereas bilateral pelvic decentralization selectively reduced the number of CGRP-IR nerves in all structures and locations. Outflow obstruction very overtly reduced the number of NOS-IR nerves in parallel with the general autonomic innervation. Thus, in the rat female urinary tract, NOS-containing nerves particularly occur in regions with sphincteric functions such as urethra and ureteric orifices. In these regions NO may exert a transmitter role, both directly or by interaction with other transmitters/modulators.