The El mouse is an animal model with genetically determined epilepsy. To elucidate the mechanism of convulsive seizures in El mice, the effects of L-glutamate and glycine on the binding of (+)[3H]MK-801 were studied in well-washed membranes from forebrains of ddY, BALB/c and El (stimulated and non-stimulated) mice. There were no significant differences in affinity (Kd) or density (Bmax) among the 4 groups of mice under basal conditions. Incubation in the presence of L-glutamate and/or glycine led to an increase in apparent density, but not in affinity. No significant change was observed in either Kd, Bmax, or the percentage increase in (+)[3H]MK-801 binding amount the 4 groups in the presence of L-glutamate and/or glycine. These results suggest that the seizure susceptibility of El mice cannot be explained by changes in affinity or density of the NMDA receptor/channel complex.