The use of evoked potentials for the evaluation of neuronal mechanisms by which convulsant drugs activate epilepsy and produce seizure has been reported by many authors. Electrophysiological effects of bemegride with augmented responsivity of brain structure to sensory stimulation is well known, especially in experiments performed with implanted electrodes in animals. After recording evoked activity from parietal scalp following median nerve stimulation before and during 12 human EEG activations by bemegride, the authors find an increase in amplitude of cortical somatosensory evoked potentials. Changes in amplitude after diazepam administration are analysed, as well as morphological changes preceding and following grand mal seizures induced by bemegride administration. This variation in amplitude of evoked responses is compared with those recorded in animals with several convulsant drugs and in man affected with progressive myoclonic encephalopathies. A common action of these agents, beyond their effects on specific neurotransmitters (perhaps mediated by a blockade of neurotransmitter-induced chloride conductance increases), is discussed.