The distribution of [3H]kainic acid (KA) binding sites in the rat CNS was determined by in vitro autoradiography. KA sites are distributed throughout the CNS gray matter in an anatomically specific pattern with telencephalic structures and the cerebellum accounting for the majority of the binding. These results, together with our previous finding that KA sites are greatly enriched at the synapse, suggest that KA binding sites are associated with select terminal fields, and hence may be involved in neurotransmission in certain CNS pathways.