The effects of acute and subchronic administration of the noncompetitive NMDA receptor antagonist MK-801 on the duration and severity of amygdaloid-kindled seizures in rats were determined to evaluate its anticonvulsant activity. Both the highest acute (1000 μg/kg) and subchronic regimens (2 × 300 μg/kg, 7 days) produced significant reductions in the seizure stage and afterdischarge duration. Although ataxia may have affected the seizure stage, MK-801 attenuated the primary afterdischarge suggesting anticonvulsant effects in the fully amygdaloid-kindled rat. Since tolerance develops to the behavioral effects of MK-801, other noncompetitive NMDA antagonists related to MK-801 seem to warrant evaluation as anticonvulsants.