In the present study, we aimed to investigate the effect of central exogenous serotonin (5-HT) on ventilation during normoxia and hypoxia. The experiments were performed in peripheral chemoreceptors intact rabbits anesthetized with urethane (400 mg/kg I.V) and alpha-chloralose (40 mg/kg I.V). For intracerebroventricular (ICV) administration of serotonin (5-HT), a cannula was placed intracerebroventricularly to the left lateral ventricle with stereotaxy. Respiratory frequency (f/min), tidal volume (VT), ventilation minute volume (VE) and systemic arterial blood pressure (BP) were recorded and mean arterial pressure was calculated (MAP). ICV administration of 5-HT (20 μg/kg) caused an increased in f/dk ,VT and VE. After ICV administration of 5-HT, breathing of hypoxic gas mixture (8 % O2 - 92 % N2) produced an increase in hypoxic respiratory responses. ICV ketanserin administration (5-HT2A/2C receptor antagonist, 10 (g/kg), in rabbits caused a decrease in f/min, VT, and VE. ICV ketanserin also prevented the stimulatory effect of 5-HT on ventilation during normoxia. In conclussion, the results of this study show that 5-HT increases ventilation during normoxia and hypoxia via 5-HT2 receptors.