Understanding depth of anesthesia is essential for the anesthesiologist. Although electroencephalogram (EEG) has been proposed and studied as a method of determining anesthetic depth, major limitations restrict its usefulness. For example, spectral edge frequency (SEF) dose not correlate well with the level of sedation. However, recently introduced bispectral index (BIS) which is derived from frequency, amplitude and coherence of the EEG is strongly correlated with clinical measurements of sedation and hypnosis. BIS monitoring may be used to guide the titration of anesthetic agents to achieve effective dosing without increasing the risk of awareness and to allow a better balance of hypnotic and analgesic administration. We report two cases of successful BIS monitoring for the measurement of intraoperative hypnotic state of patient during propofol target controlled infusion (TCI).