One of the more difficult psychopharmacologic aspects of current clinical psychiatry is finding a neuroleptic drug that adequately treats delusional states. Furthermore, many chronic schizophrenics remain resistant to standard antipsychotic medication, and clozapine is effective in only 30% to 50% of refractory cases. In addition, clozapine has several serious side effects and is expensive. We have determined that pimozide is clearly effective in Tourette's syndrome, maintenance schizophrenia, and some delusional disorders. We further demonstrate that the drug is likely to be effective in the treatment of the negative symptoms of schizophrenia and other delusional states. In addition, we suggest that a trial of pimozide may be indicated before giving clozapine to treatment-resistant schizophrenic patients. The side effect that probably most limits pimozide's current use is the possible production of ECG abnormalities. This side effect does not seem to be a realistic clinical concern, however, if the patients are properly screened and the pimozide dose is maintained at or below 20 mg/day.