We have characterized a second member (delta-2) of a new class of subunits for the ligand-gated excitatory amino acid receptor superfamily. The sequence of delta-2 exhibits an average identity of 25% and 18.5% to the non-NMDA and NMDA receptor subunits, respectively. The rat delta-2 gene is expressed predominantly in Purkinje cells of the cerebellum whereas only low levels of delta-1 transcripts are found in the adult brain. However, delta-1 gene expression undergoes a pronounced developmental peak, with particularly high mRNA levels in the caudate putamen of late embryonic/early postnatal stages.