Using a newly developed technique, based on microdialysis, which allows cellular uptake of glutamate and aspartate to be studied in awake animals, we investigated uptake of glutamate and aspartate in the hippocampal formation of rats during limbic seizures induced by systemical administration of kainic acid (KA). With [14C]mannitol as an extracellular reference substance, the cellular extraction of the test substance [3H]D-aspartate was measured at different stages of seizure-activity. The results were compared to those obtained in a sham operated control group. During severe generalized clonic seizures, the extraction of [3H]D-aspartate was increased by 17%. The increase in uptake of [3H]D-aspartate was accompanied by a 24% increase in the extracellular level of aspartate, as obtained by conventional microdialysis. No significant changes were observed in the extracellular level of glutamate. The results indicate that during KA-induced seizures, uptake of glutamate and aspartate is increased, possibly aimed at maintaining the extracellular homeostasis of these two excitatory amino acids.