Twenty-two plasma amino acids were determined by means of ion-exchange chromatography in 16 previously untreated patients with generalized idiopathic epilepsy and in some of their first-degree relatives (26 subjects), and the results were compared with those obtained from a group of 50 healthy controls. The patients were subsequently treated with valproic acid for one month and then reexamined. In the epileptic subjects, statistical analysis showed significant alterations in the plasma levels of a group of amino acids, including the four associated with neuro-transmission (aspartate, glutamate, glycine, taurine); aspartate, glutamate and glycine levels were also altered in the first-degree relatives. Valproic acid therapy did not affect amino acid levels. If further confirmed, these alterations might be considered possible neurochemical markers of epilepsy.