An intraventricular injection of 6-hydroxydopamine, which produced a marked decrease of catecholamines in the forebrain, significantly lowered the electroconvulsive threshold in rats. The anticonvulsant effect of carbamazepine was also significantly reduced in the animals treated with 6-hydroxydopamine. The results are consistent with the hypothesis that brain catecholamines may play an important role in seizure susceptibility as well as in the anticonvulsant activity of carbamazepine in rats.