Male Wistar rats administered repetitively with pentylenetetrazol developed a dose-dependent enhancement of seizure behaviour referred to as pentylenetetrazol kindling. After a daily dose of 40 mg pentylenetetrazol/kg or physiological saline (control rats) injected intraperitoneally for a period of two weeks, hippocampal tissue was studied autoradiographically for high-affinity uptake of [3H]glutamate and, by activity staining, for aspartate aminotransferase and glutamate dehydrogenase. Most prominent changes were found in neuropil areas known to be endowed with glutamatergic structures. The uptake capacity of glutamate decreased by 48% (maximum rate), whilst activities of aspartate aminotransferase and glutamate dehydrogenase elevated to 140 and 130%, respectively. Cytochrome c oxidase activity was found to be unaffected. The findings indicate an important role of factors of the glutamate metabolism in the kindling process with respect to the production, utilization, and availability of transmitter glutamate.