In this study, in situ hybridization techniques were employed to map the distribution of enteric neurons which express mRNA for the glutamate N-methyl-D-aspartate receptor 1 (NMDAR1). We hybridized tissue sections from the stomach, duodenum, ileum and descending colon of adult rats with a 1.43-kB riboprobe cleaved from a clone of the NMDA receptor. Enteric neurons expressing the mRNA were found in both myenteric and submucosal ganglia at each of the sampling sites. Possible functions of NMDA receptors on enteric neurons are discussed.