Hypothalamus is a site of integration of the hypoxic and thermal stimuli on breathing and there is evidence that serotonin (5-HT) receptors in the anteroventral preoptic region (AVPO) mediate hypoxic hypothermia. Once 5-HT is involved in the hypoxic ventilatory response (HVR), we investigated the participation of the 5-HT receptors (5-HT 1 , 5-HT 2 and 5-HT 7 ) in the AVPO in the HVR. To this end, pulmonary ventilation (V˙E) of rats was measured before and after intra-AVPO microinjection of methysergide (a 5-HT 1 and 5-HT 2 receptor antagonist), WAY-100635 (a 5-HT 1A receptor antagonist) and SB-269970 (a 5-HT 7 receptor antagonist), followed by 60min of hypoxia exposure (7% O 2 ). Intra-AVPO microinjection of vehicles or 5-HT antagonists did not change V˙E during normoxic conditions. Exposure of rats to 7% O 2 evoked typical hypoxia-induced hyperpnea after vehicle microinjection, which was not affected by methysergide. WAY-100635 and SB-269970 treatment caused an increased HVR, due to a higher tidal volume. Therefore, the current data provide the evidence that 5-HT acting on 5-HT 1A and 5-HT 7 receptors in the AVPO exert an inhibitory modulation on the HVR.