The effect of phenobarbital (PB) on the cytotoxicity induced by the excitatory amino acids (EAAs) glutamate, aspartate, N-methyl-D-aspartate (NMDA), kainate (KA), quisqualate (QA) and RS-alpha-amino-3-hydroxy-5-methyl-4-isoxazolopropionate (AMPA) was investigated in cultured cerebral cortex neurones. PB (100 microM) completely protected against the total cytotoxic damage induced by KA, whereas it had no such effect on the toxicity induced by any of the other EAAs. The IC50 for the inhibition of the KA induced toxicity was 56 microM. Furthermore, PB completely blunted the large increase in O2 uptake in the neurones seen during exposure of the cultures to KA. Since exposure of the cells to PB alone did not affect the basal O2 consumption in the cultures, these results suggest that PB directly interacts with the KA receptor or, alternatively, with processes which selectively are coupled to activation of the KA receptor but not to activation of other types of EAA receptors.