The effect of the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX) on N-methyl-D-aspartate (NMDA)-evoked seizures was studied in C57BL/6 mice (20/group). Animals were injected i.p. either with CPA (0.5, 1, 2 mg/kg) or CPX (1, 2 mg/kg) 15 min prior to administration of NMDA (30, 60, 125 mg/kg). Administration of NMDA alone resulted in a complete locomotor arrest at 30 mg/kg, while clonic/tonic seizures and progressively increasing mortality were seen at higher doses. Prior administration of CPA resulted either in a delay of seizure onset and unchanged mortality (0.5 mg/kg CPA, 60 mg/kg NMDA) or in elimination of tonic episodes and a significant reduction in postictal mortality (1, 2 mg/kg CPA; 60, 125 mg/kg NMDA). Pretreatment with CPX at either 1 or 2 mg/kg eliminated locomotor depression in animals injected with NMDA at 30 mg/kg. At 60 mg/kg NMDA, the effect of CPX administration resulted in mortality equivalent to that seen with 125 mg/kg NMDA administered alone. The results indicate that A1 receptor agonists may protect against NMDA-evoked seizures and that the adenosine A1 receptor may be directly involved in these actions.