Seventeen epileptic patients suffering from generalized idiopathic epilepsy who underwent antiepileptic treatment with sodium valproate (NaVPA) for the first time were studied. The EEG was recorded at rest with eyes closed (EC), during blocking reaction, fixation and mental arithmetic tasks. The computerized EEG study, performed before and after therapy, utilized spectral analysis; data underwent statistical evaluation including ANOVA and correlation analysis. Before NaVPA therapy, a significant decrease of beta1 and beta2 relative power, compared with control subjects, was observed in epileptic patients at rest with EC, whereas fast activity increased during mental tasks. After treatment, no significant variations in fast activity were observed during tasks, with a pattern similar to that observed in the control population. Therefore, considering the effect of NaVPA primarily on fast activity, which reflects rather well preserved mental functioning processes, it is possible to hypothesize that the drug interferes positively with mental activities.