Sleep variables and psychiatric symptoms were investigated in 6 male chronic schizophrenic outpatients. The patients were being treated with benzodiazepine (BZD) hypnotics for more than 8 weeks, and BZDs were replaced with zopiclone (ZPC) 15 mg/day. Polysomnographic examinations, subjective sleep assessments and BPRS scoring were performed during BZD therapy and at the end of 8 weeks of ZPC therapy. The doses of neuroleptics and anticholinergic agents remained fixed throughout the study. The amount of slow-wave sleep (SWS) was markedly small and that of stage 1 sleep was moderately large during BZD therapy. The amount of stage 1 was smaller and that of stage 2 was larger during treatment with ZPC than BZDs. There were no significant change in the amount of SWS between the treatment. Half of the patients exhibited a sleep-onset REM period (SOREMP) during ZPC therapy. Both total BPRS score and negative symptom score were lower during treatment with ZPC than BZDs. These results suggest that ZPC may be more beneficial in treating schizophrenic insomnia than BZD hypnotics and that reduced SWS and SOREMP may be partly involved in the pathophysiology of schizophrenia.