Abstract: This invention consists of a method and apparatus for separation of the facial electromyogram (EMG) and the electroencephalogram (EEG) implemented in an index for assessing the level of consciousness during general anaesthesia. The surface EEG/EMG signal is collected from three electrodes (1) positioned middle forehead, left forehead and on the cheek, 2 cm below the middle eye line. The novelty of this method and apparatus is that the EMG is separated from the EEG to a such extent that a more reliable feature extraction of the EEG can be carried out, without significant interference from the EMG. This is necessary for example when designing an EEG based index for assessing the level of consciousness during general anaesthesia. The method could be implemented in other devices where a high quality EEG is required. The apparatus consists of electrodes and cable connected to an amplifier, a D/A-converter, a microprocessor which executes the processing and displays the result on a display.