Anticonvulsant action of MK-801, a novel noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptor, was examined in genetically epileptic E1 mice. Systemic injection of MK-801 (0.1-1.0 mg/kg) potently suppressed generalized tonic-clonic convulsions of in a dose-dependent manner (ED50, 0.17 mg/kg). This anticonvulsant effect of MK-801 appeared at a dose which did not induce any obvious behavioral changes. Following the administration of a fully anticonvulsant dose of MK-801 (1 mg/kg), amino acid analysis revealed a significantly elevated level of glycine in the hippocampus. Levels of other amino acids including glutamate, aspartate, taurine, glutamine, alanine, and gamma-aminobutyrate were not changed either in the hippocampus or in the cerebral cortex. This study suggests that NMDA system may play an essential role in seizure-triggering mechanisms in E1 mouse.