Second-generation antipsychotic medications have become popular as a treatment for schizophrenia. The authors investigated 25 chronic subjects who had previously been treated with high-dose antipsychotic polypharmacy without amelioration. All patients had a history of having been treated with an antipsychotic polypharmacy regimen of the total daily chlorpromazine equivalent dose exceeding 1000 mg/day for more than 6 weeks. They were subsequently switched to a second-generation antipsychotic monotherapy. Other psychotropic medications were simplified at the same time. For successful patients whose symptoms showed at least minimal improvement, the medical chart was reviewed retrospectively. After completed switching, the patients were followed up for 12 weeks, when final evaluation was made. The Global Assessment of Functioning score improved from 32 to 47. The number of antipsychotic medications and total psychotropic medications were significantly reduced from 3.5 to 1.1 and 6.8 to 2.6, respectively. Also, the antipsychotic dose was significantly minimized from 2203 to 619 mg/day. Eleven of eighteen inpatients were discharged and the other four were better enough to be ready for discharge. By showing successful cases, the authors suggest a possibility of antipsychotic monotherapy with a second-generation agent even for those patients who had been treated with high-dose antipsychotic polypharmacy in vain.