In the present paper, the influence of the adenosine receptor agonist N6-(l-2-phenylisopropyl)adenosine (L-PIA) and of the adenosine receptor antagonist caffeine on the epileptiform and neurotoxic effects of N-methyl-d-aspartate (NMDA) has been tested in rat hippocampal slices. Slice superfusion with 1 microM NMDA changed within 30 min the control CA1 field potentials into an epileptiform bursting in all experiments. Slice superfusion with 0.5-1 microM L-PIA or 50-100 microM caffeine plus 1 microM NMDA inhibited or potentiated, respectively, the CA1 epileptiform bursting duration with respect to a slice superfusion with 1 microM NMDA alone. Slice superfusion with 50-100 microM NMDA induced within a few minutes the appearance of short-lived (1-2 min) additional epileptiform population spikes, followed by an irreversible disappearance of the CA1 population spike. Slice superfusion with 50 microM of the NMDA antagonist dizocilpine (MK801) plus 50-100 microM NMDA prevented in all experiments the irreversible disappearance of the CA1 population spike with respect to a slice superfusion with 50-100 microM alone. Neither in a slice superfusion with 0.5-1 microM L-PIA plus 50-100 microM NMDA nor in a slice superfusion with 50-100 microM caffeine plus 50-100 microM NMDA did this effect occur. The results demonstrate that adenosine receptor ligands modulate the epileptiform but not the neurotoxic effects of NMDA.