The modifications of the electroencephalic patterns in 24 childrens with daily epileptic seizures treated by benzodiazepine derivatives were studied. The electroencephalographic findings during the longitudinal therapeutic follow-ups disclose important modifications of the subcortical mechanisms involved in the production of the convulsive seizures and paroxistical discharges. These facts are in accordance with the hypothesis that benzodiazepine derivatives act upon the non-specific thalamic reticular system. The benzodiazepine derivatives are more active upon the inhibitory system related to the thalamocortical projection system. Two hypothesis are discussed: 1 — the drugs act upon chemoreceptors present in the thalamic reticular system; 2 — the act indirectly, depressing some elements of the limbic system and modifying in this way the feed-back of subcortical circuits which discharge upon hyperactive centrencephalic neurons.