Objective:Coherence analysis of the EEG is used to study the synchrony or coupling between cortical areas underlying the electrodes. However,the effects of intravenous anesthetics on EEG coherence have not been defined. Method: Forty patients were administered with intravenous thiopental (5mg/kg),propofol (2.5mg/kg ), ketamine(4mg/kg)or fentanyl(10?g/kg). The changes of coherences in total and in a given frequency band of the EEG(?.?.?.?) were measured with an AXON Systems Sentinel-4 Neurological monitor between two pair electrodes(Cz-F_7 vs Cz-F_8 and Cz-A_1 vs Cz-F_2). Result: The anesthetics had significantly different effects on the coherence by either increase or decrease. The variability of the coherences had no regular pattern,and no relationship to excitement or depression of the anesthetics and to potency of them. Conclusion:Each anesthetic above selectively depresses and excites generators of the EEG in quite different ways.