Recent reports in clinical literature have suggested an antiepileptic effect of the xanthine oxidase inhibitor Allopurinol (ALL) when added to traditional drugs. However, other reports have failed to confirm beneficial effects of this drug. In view of these conflicting results, we have carried out a study aimed at evaluate the effects of ALL in different forms of epilepsy. The result that ALL possesses some antiepileptic effects in Lennox-Gastaut syndromes, characterized by numerous and severe fits, while it is scarcely effective in other forms of epilepsy, suggests that ALL might be involved in the purinergic-mediated inhibition similar to that described in experimental "status epilepticus" studies in animal models.