In locally anesthetized, paralyzed cats with bilateral conjugated estrogen (CE)-induced foci in sensory motor cortex, electrographic activity was characterized by 2 to 3 Hz spike and slow wave discharge. Commonly used anti-petit mal drugs (esthosuximide, trimethadione, acetazolamide and diazepam) all reduced CE-induced spike wave activity while diphenylhydantoin converted such activity into 9 to 12 Hz polyspike bursts separated by periods of interictal silence. Correlation appears to exist, therefore, between the ability of the drug to reduce CE-induced spike wave activity and its clinical utility in petit mal epilepsy. In addition to the above compounds, five drugs of less proven utility were evaluated. Of these, two benzodiazepine derivatives (clonazepam and clorazepate) were found to exert a potent and prolonged depressant action on CE-induced activity. The relation of CE to clinical petit mal epilepsy and the potential usefulness of CE as a laboratory model for the evaluation of anti-petit mal drugs are discussed.