The vomeronasal organs of female Wistar rats after the intraperitoneal administration of ketanserin and propranolol prior to sacrifice were exposed to sprayed urine of male Wistar rats. To explore the effects of these antagonists, we studied Fos-immunoreactive (Fos-ir) structures, which correlate with cellular activity, in the accessory olfactory bulb of female rats after the vomeronasal organ was exposed to urine. After the administration of 3 mg/kg ketanserin, the expression of Fos-ir cells in the periglomerular cell layer in response to male Wistar urine was inhibited, while that in the mitral/tufted cell and granule cell layers was not changed. The administration of 20 mg/kg propranolol inhibited the expression of Fos-ir cells in all three layers. These results suggest that serotonin and noradrenaline are likely involved in the modulation of the expression of Fos-ir cells in response to the urine in the accessory olfactory bulb.