The effects of neuropeptide Y (NPY) on motility of the proximal stomach was examined in anaesthetized rats. Intragastric pressure (IGP) was measured using a balloon situated in the proximal part of the stomach. The administration of NPY into the fourth ventricle induced relaxation of the proximal stomach in a dose-dependent manner. Administration of an Y1 receptor (Y1R) agonist [Leu³¹, Pro³⁴] NPY induced a larger relaxation than NPY. The administration of an Y2 receptor agonist (NPY 13 - 36) did not induce significant changes in motility. Microinjections of [Leu³¹, Pro³⁴] NPY into the caudal part of the dorsal vagal complex (DVC) induced relaxation of the proximal stomach. In contrast, similar injections into the intermediate part of the DVC increased IGP of the proximal stomach. The administration of NPY into the fourth ventricle did not induce relaxation after bilateral injections of the Y1R antagonist (1229U91) into the caudal DVC. These results indicate that NPY induces relaxation in the proximal stomach via Y1Rs situated in the DVC. Since bilateral vagotomy below the diaphragm abolished the relaxation induced by the administration of NPY into the fourth ventricle, the relaxation induced by NPY is probably mediated by vagal preganglionic neurons. The intravenous injection of atropine methyl nitrate reduced the relaxation induced by the administration of NPY, therefore, the relaxation induced by NPY is likely mediated by peripheral cholinergic neurons.