An in vitro preparation has been developed in which epileptogenesis in mammalian central nervous system tissue may be studied. Addition of sodium penicillin to the medium bathing slices of guinea pig hippocampus induced epileptiform activity similar to that seen in hippocampal penicillin foci in vivo. Epileptiform events were recorded as synchronous field potentials and correlated cellular bursts that ocurred spontaneously and could be triggered by orthodromic stimulation. Intracellular recordings revealed that bursts were generated from large depolarization shifts in some neurons, while in others, burst discharges had little underlying baseline depolarization. This finding, and the presence of fast prepotentials in penicillin‐treated preparations, suggested the involvement of dendritic activity in generation of epileptiform discharges.