Eight patients in deep coma after cardiopulmonary arrest showed EEG activity of alpha frequency. This was more anterior and widespread than the normal alpha rhythm. It was unreactive to auditory, noxious, or photic stimuli in six patients, but in two other subjects changes were induced by noises and noxious stimuli. Patterns resembling stage I sleep developed in three patients. Serial EEGs performed on six individuals showed that low-voltage delta activity supervened. All eight patients died. Neuropathologic studies demonstrated cerebral cortical anoxic lesions, but none had gross brainstem changes. Histologic examination of the basal ganglia and thalamus in four and of the brain stem in three cases was unremarkable.