Sixteen-channel electroencephalograms (EEGs) were obtained from seven patients with the “locked-in” syndrome, a condition of mute quad-riplegia with preservation of consciousness, readily mistaken for deep coma. The EEGs of all but one patient showed, for most of the time, a reactive alpha or theta rhythm consistent with consciousness. Some subjects showed minor focal or bilateral disturbances in the theta or fast delta range. An alpha-like rhythm may occur in truly comatose patients, but this activity usually is reported to be unresponsive to most alerting stimuli. Autopsies were done on six of these patients and all had ventral pontine damage. We suggest that the EEG permits a rapid, simple way of diagnosing the “locked-in” state.