Glutamate is one of the most common excitatory neurotransmitter in the central nerve system. It has been shown that central glutamate N-methyl-D-aspartate (NMDA) receptors are important components of the cardiorespiratory regulation. On the other hand, the presence of NMDA-type glutamate receptors has been demonstrated in many peripheral tissue as lungs, airways and carotid bodies. However the effect of those NMDA receptors on cardiorespiratory parameters is not completely considered. The purpose of this study was to investigate the effect of systemic glutamate NMDA receptors on cardiorespiratory parameters during both normoxia and acute hypoxia in rabbits. In this study 8 adult albino rabbits weighing avarege 2.7 ± 0.4 kg were used. The rabbits were anesthetized with urethane (400mg kg-1, i.v) and alpha-chloralose (40 mg kg-1, i.v). Tracheotomy was performed and the tracheal cannula connected to an inspiratory-expiratory valve was inserted into the trachea. The right femoral arterial catheter was used to collect arterial blood samples. Experiments were terminated by i.v injection of an overdose (500 mg kg-1) of sodyum pentobarbitone. Tidal volume (VT), respiratory frequency (f/min), ventilation minute volume (VE), mean arterial pressure (BP) and heart rate (HR) were recorded during the breathing of the normoxic and hypoxic (8% O2 – 92% N2) gas mixtures, before and after the administration of the i.v MK-801 (glutamate NMDA receptor antagonist) in anaesthetized rabbits. At the end of each experimental phase, PaO2, PaCO2, and pHa were measured. Values are presented as means ±S.E.M., compared by Wilcoxon-Matched Paired t- test. The injection of MK-801 (0.9 mg kg-1, i.v) during normoxia caused a decrease in BP (p<0.01), HR (p<0.001), VT (p< 0.01) and VE (p<0.01) values, whereas it caused an increase in f/min (p<0.001). After MK-801 administration, when hypoxic gas mixture was breathed to rabbits significant decreases in f/min (p<0.01), VE (p<0.05) and HR (p<0.01) were observed. The elevation response in BP seen during acute hypoxia was completely abolished by MK- 801 administration. Our findings suggested that glutamate has a excitatory effect on both blood pressure and ventilatory activity via NMDA-type peripheral glutamate receptors during normoxic and acute hypoxic gas breathing. In line, when MK-801 was used to lower blood pressure, its depressor effect on ventilation should be taken into consideration in hypoxic conditions.