Epileptic afterdischarges induced by electrical stimulation of the sensorimotor cortex as well as minimal metrazol seizures are characterized by EEG spike-and-wave rhythm and nearly the same motor pattern of clonic seizures. The action of ethosuximide on these two models was tested in adult rats with implanted electrodes. Cortical afterdischarges remained practically uninfluenced by ethosuximide (62.5 or 125 mg/kg i.p.) whereas minimal metrazol seizures were suppressed in a dose-dependent manner (doses of 31.25, 62.5 and 125 mg/kg i.p. were used). Present results in connection with recent data on the abolition of spike-and-wave rhythm elicited by low systemic doses of pentylenetetrazol suggest that spike-and-wave rhythm does not represent a single entity.