BACKGROUND Neuropeptides are important in the regulation of vascular functions. The purpose of the present study was to investigate the distribution of perivascular nerve fibers containing neuropeptides and nitric oxide synthase (NOS) in the rat ophthalmic artery. METHODS Neuropeptide- and NOS-containing nerve fibers in the rat ophthalmic artery were identified using immunocytochemistry following unilateral parasympathectomy (electrocoagulation of the sphenopalatine ganglion) and sympathectomy (superior cervical ganglionectomy). The contralateral artery was used as control. RESULTS Nerve fibers containing vasoactive intestinal peptide (VIP), neuropeptide Y (NPY) and NOS were abundant in the wall of the ophthalmic artery. Nerve fibers containing calcitonin gene-related peptide and substance P were scarcer. Following destruction of the sphenopalatine ganglion there was no discernible change in the density of VIP- and NPY-immunoreactive fibers, while the majority of the NOS-containing fibers disappeared. Following sympathectomy the NPY-containing nerve fibers were almost completely eliminated, whereas VIP- and NOS-containing fibers were unaffected. CONCLUSIONS The present study demonstrates that the sphenopalatine ganglion is the main contributor of NOS-containing nerve fibers to the rat ophthalmic artery. In contrast, this ganglion apparently is of little importance as a source of VIP-immunoreactive nerve fibers to the artery, demonstrating different origins of the majority of the VIP-and NOS-containing fibers to this artery. The NPY-containing nerve fibers in the rat ophthalmic artery emanate mainly from the superior cervical ganglion.