Experience with 25 isoelectric electroencephalograms obtained during the past ten years with the 25 "respirator brains" examined during the past three years is presented. Characteristic neuropathological features of the respirator brain consist of severe brain swelling, gray to hemorrhagic discoloration, marked softening, and both anoxic necrosis and autolysis of neurons. An isoelectric EEG, defined as complete loss of cortical electrical activity with maximal amplification, if sustained for an hour or more under appropriate clinical circumstances, is highly suggestive of cerebral death.