ABSTRACT.In some respects the EEG of sleep and coma may be comparable and the purpose of monitoring a sleeping subject and a comatose patient by spectral array are similar–reduction of data, observance of slow EEG changes with time at a glance, and detection of features in the EEG of sleep and coma without reference to the concept of sleep stages. This is especially appropriate when sleep scoring landmarks and phasic events such as rapid eye movements, sleep spindles, or K-complexes are not well defined or absent. Discussed in this paper are the technique and validation of recording with density spectral array in sleep and coma. Results from a validation study of density spectral array compared to simultaneous polygraph sleep recordings in ten normal subjects are presented and used as a control and comparison for the density spectral array recordings of comatose patients.