Although large quantities of glutamate are found in the carotid body, to date this excitatory neurotransmitter has not been assigned a role in chemoreception. To examine the possibility that glutamate and its NMDA receptors play a role in acclimatization after exposure to cyclic intermittent hypoxia (CIH) we exposed male Sprague-Dawley rats to cyclic hypoxia or to room air sham (Sham) for 8 hours/d for 3 weeks. Using reverse transcriptase PCR (RT-PCR), Western Blot and immunohistochemistry, we found that ionotropic NMDA receptors including NMDAR1, NMDAR2A, NMDAR2A/2B are strongly expressed in the carotid body and co-localize with tyrosine hydroxylase in glomus cells. CIH exposure enhanced the expression of NMDAR1and NMDAR2A/2B, but did not substantially change the level of NMDAR2A. We assessed in vivo carotid sinus nerve activity (CSNA) at baseline, in response to acute hypoxia, in response to infused NMDA, and in response to infused endothelin-1 (ET-1) with and without MK801, an NMDA receptor blocker. Infusion of NMDA augmented CSNA in CIH (124.61 ± 2.64 % of baseline) but not in Sham-exposed rats. Administration of MK801, an NMDA receptor blocker did not alter baseline activity or response to acute hypoxia, in either CIH or Sham animals but did reduce the effect of ET-1 infusion on CSNA (CSNA after ET-1 160.96 ± 8.05 % of baseline; ET-1 after MK801 118.56 ± 9.12%). We conclude that 3-week CIH exposure increases expression of NMDA functional receptors in rats suggesting glutamate and its receptors may play a role in hypoxic acclimatization to cyclic intermittent hypoxia.