Background: Monitoring of " Depth of anesthesia " is an ongoing problem in anaesthesia. In this study, the author has compared the bispectral index (BIS) and Anemon monitor for monitoring depth of anesthesia in propofol or isoflurane anesthesia. Methods: Anemon-1 and BIS index were obtained from 24 patients (ASA I, II) during general anesthesia with propofol or isoflurane. For patients in the propofol group, anesthesia was induced with fentanyl 100 ㎍ followed by propofol 2 mg/kg. For patients in the isoflurane group, anesthesia was induced with thiopental 5 mg/kg. The author observed changes of these values at 5 major times: before induction, during induction, after induction, at skin incision, before extubation, after extubation. Results: The anemon index showed a significant increase during induction (propofol group: 86.9±26.4, isoflurane group: 106.0±18.6) and at skin incision (propofol group: 89.9±22.7, isoflurane group: 92.0±23.1), but this did not correlate with the level of consciousness. The BIS index showed a significant decrease in the score after induction (propofol group: 55.0±9.6, isoflurane group: 61.0±17.2), but no response to surgical stimuli. Conclusions: BIS had a good correlation with level of consciousness. The Anemon-1 index was recognized to reflect invasive stimulus. As the BIS and Anemon-1 had no correlation, it was not possible to assume changes of each index from the other. Both the anemon-1 index and BIS are useful to monitor the anesthesia level during surgery. (Korean J Anesthesiol 2001; 41: 531-537)