Objective: The goal of this study was to investigate the changes in the responses to auditory stimuli, which were sorted according to the Bispectral Index (BIS) during sleep. This is the first known research study that incorporated full-scale analysis of sleep auditory evoked potentials (AEP) under the scope of BIS. Material and Methods: The measurements were conducted in twelve subjects (18-32 ages, mean: 24.5 +/- 4.1; 2 female). Recordings were done by using NuAmps 40 channel system [electroencephalography (EEG), electrooculography (EOG), and chin electromyography (EMG)], auditory stimulation unit, video and BIS monitor. Sleep data was acquired while (1500 Hz, 80 dB and 500 ms) auditory stimulations were applied into the ear channels (etymotic). The continuous EEG data were grouped according to the BIS index. In this sub-group of recordings, AEPs were analyzed. The evolution of N1, P2, N300, P450, N550 and P900 waveforms recorded from Cz electrode were investigated with regard to correlation of BIS and sleep stages. Results: The reduction of BIS values were followed by the decrease of NI component, whereas N300 and P900 components were found to be increased (Wilcoxon, p<0.05). AEPs dynamically evolved according to the changes in BIS values. The present findings support and advance the outcome of classical designs, which are based solely on the system Rechtschaffen & Kales (R&K) system. Conclusion: The present study investigated sleep states in extended number of levels with the BIS system, which provided higher time resolution. Based on the results, BIS may be suggested as a useful tool for sleep dynamic research studies also in pathological states
