Very few controlled clinical trials have been assessing the interaction of antipsychotics and antiepileptics. However, schizophrenic patients frequently receive a combination therapy consisting of haloperidol and carbamazepine. The data for this treatment strategy are contradictory and may depend on the initial plasma concentration of the antipsychotic. There is convincing evidence that after addition of carbamazepine the plasma concentration of neuroleptics drops due to hepatic enzyme induction. In this study, we treated 18 schizophrenic patients either with haloperidol alone or in combination with carbamazepine. The use of carbamazepine was associated with a dramatic fall in haloperidol plasma levels and a worse clinical outcome compared to the monotherapy group. These results, together with a review of the literature, lead us to the conclusion that there are no obvious advantages of carbamazepine co-medication in schizophrenia compared to an optimized neuroleptic monotherapy.