Kainic acid (KA)-sensitive glutamate sites have been investigated by receptor autoradiography and in situ hybridisation histochemistry (ISHH) to evaluate their relationship to specific high-affinity KA receptors identified in molecular biological studies. Autoradiography with [3H]KA in the presence of the AMPA-selective antagonist NBQX (1 microM) revealed a widespread distribution of receptors through brain, especially in neocortex, hippocampal CA3, corpus striatum and granule cell layer of cerebellum. Specific binding was insensitive to the AMPA-selective agonist, S-5-fluorowillardiine, but inhibited by kainoids in a manner suggestive of receptor heterogeneity. Expression of the KA-2 receptor subunit mRNA by ISHH was also localised in hippocampal CA3 and cerebellar granule cells, suggesting some high-affinity native KA receptors labelled by [3H]KA were likely to include the KA-2 subunit in their heteromeric assembly.