Reduction of [Mg²⁺]_o induced spontaneous epileptiform activity consisting of 40–100-ms bursts of population spikes in hippocampal slices. This activity disappeared from area CA₁ when the connections to area CA₃ were cut, but persisted in isolated minislices of area CA₃. Spontaneous activity was also observed in the dentate gyrus, provided that the connections to the subiculum and entorhinal cortex (EC) were intact. In the parasubiculum and EC longer lasting epileptiform events were observed which resembled seizure-like behaviour. The epileptiform activity was completely suppressed by 2-aminophosphonovalerate (30 μM) suggesting that N-methyl-d-apartate receptors for excitatory amino acid transmitters participate in the generation of this activity. These findings show that the EC possesses properties which permit the generation of seizure-like activity in contrast to the hippocampus where the activity resembled recurrent interictal events.