The anatomical localization of the increase in omega 3 (peripheral type benzodiazepine) binding site densities (an index of glial reaction) following intraperitoneal injection of convulsant doses of kainic acid has been studied by autoradiography in the rat brain. Consistent increases in omega 3 site densities were observed in the olfactory, piriform and entorhinal cortices, amygdaloid nucleus, hippocampal formation and thalamus. In the hippocampal formation, the most pronounced increases were seen in the stratum lucidum of the CA3 field and in the stratum oriens and pyramidale of the CA1 and CA2 fields. This pattern of changes in omega 3 site densities closely paralleled the pattern of neuropathological alterations (assessed by histological methods) observed in these brain regions. Thus, omega 3 site autoradiography may provide a sensitive and reliable index of the neuronal damage resulting from kainic acid administration.