In-situ hybridization (ISH) has been used to determine the distribution of the mRNA encoding a non-NMDA glutamatergic receptor subtype in rat and human brain. In the rat, signal is concentrated over neurons in hippocampus and cerebellum, with moderate labelling of neocortex and diencephalon. In human brain, a similar hippocampal and cerebellar distribution is seen, although with lower overall levels. Quantitative comparison between normal and Alzheimer's disease (AD) brain reveals a modest increase of this mRNA in AD subiculum and CA4 hippocampal field with no change in cerebellum. The significance of the increase is discussed in relation to other data suggesting glutamatergic involvement in AD.