Some patients diagnosed as schizophrenic report persistent polymodal hallucinosis following a period of extensive hallucinogenic drug abuse unrelieved by the usual antipsychotic drugs. In this open study, carbamazepine (Tegretol, an anticonvulsant) was administered to three patients with polymodal hallucinosis which had failed to diminish on antipsychotic drugs alone. All three patients showed a marked to complete reduction in symptomatology.