Expression of the gene coding for the NR1 subunit of the N-methyl-D-aspartate (NMDA)-type of glutamate receptor was investigated in the developing rat brain. Peak NR1 gene expression in the whole brain occurred at approximately postnatal day (P) 10 with a second increase in the adult. To determine the ontogenic expression in the various brain regions, the expression of NR1 at P2, P10 and P60 was compared. The regional studies indicated increased expression at P60 in the cerebellum. In the midbrain and diencephalon, levels of expression at P10 and P60 were higher than at P2, while in the hippocampus, expression at P10 was significantly higher than at either P2 or P60. Expression in the other brain regions was constant over the period studied. These data indicate a region-specific expression of NR1 in the central nervous system during ontogeny.