The nucleus of the tractus solitarius (NTS) is a primary termination zone for laryngeal, gustatory, cardiovascular, respiratory, gastrointestinal, and other visceral afferents. Although considerable information is available on the neurochemical aspects of the NTS in general, very little is known about glutamate receptors that may underlie many of the different functions mediated by the NTS. In addition, most previous glutamate receptor distribution studies were performed in the rat, whereas the cat, the subject of many physiological experiments involving the NTS, has received little attention. In the present study, the immunohistochemical distribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-selective glutamate receptor subunits (GluR1, GluR2/3, GluR4) and the N-methyl-D-aspartate (NMDA) receptor subunit NR1 in the cat caudal brainstem was investigated by using subunit-specific antibodies. In the NTS, statistically significant differences were seen in the distribution of each antibody. Highest labeling was seen for GluR2/3 in most subnuclei, whereas GluR1-immunoreactive neurons were found more frequently than were NR1- or GluR4-immunoreactive neurons. GluR1 immunolabeling was particularly high in the interstitial subnucleus, whereas GluR2/3 immunolabeling was particularly high in the intermediate subnucleus. Qualitatively, labeling for GluR4 was most common in glia. The present results indicate that glutamate receptors show different subunit distributions in the subnuclei of the NTS and in other adjacent structures. This finding suggests that neurons in these structures are designed to respond differently to excitatory input.