The efficacy of ceruletide as a supplement in treating schizophrenics was tested by monitoring the Brief Psychiatric Rating Scale (BPRS) and the EEG. 2. Eight male inpatients with schizophrenia were administered fixed doses of neuroleptics during the study. 3. A control EEG recording and BPRS scoring were done before ceruletide administration. 4. Doses of 0.8 micrograms/kg/week of ceruletide and of placebo were given intramuscularly in a double-blind, crossover design for 3 consecutive weeks, and no treatment followed for 1 week. 5. EEG recordings and BPRS scoring were carried out once weekly. There were no significant differences in the total BPRS scores or the scores of each item between ceruletide and placebo. 6. With ceruletide treatment, the power values of the frontal EEGs increased in the whole bands but only in the first week. 7. The EEG values in the occipital area increased in alpha and beta activities slightly in the third week and markedly in the fourth week. 8. The power values in the right temporal area decreased in fast beta activity in the second and third weeks but increased in alpha activity in the third and fourth week. 9. The power of the left temporal area increased in both alpha and beta bands in the second week, and this continued to the fourth week. 10. These results suggest that treatment with ceruletide might fail to improve the symptoms of schizophrenics but does affect their EEGs, and that ceruletide may have a delayed effect.