The cerebral function monitor (CFM) is a portable electronic device that processes and records bipolar cortical electrical signals derived from two parietal scalp electrodes. Specific filtering and electronic rectification permit tracings of high quality to be obtained at any location, even where electrical interference and personal movements may render the conventional EEG difficult to interpret. In a comparison study of patients with clinically apparent brain death, CFM tracings that revealed no cerebral electrical activity correlated perfectly with isoelectric EEGs performed in a neurophysiology laboratory in 10 patients who manifested signs of absent brain stem function, apositive 3-min apnea test, and severe hypotension. All patients had a terminal cardiac arrest within 17 days of onset of coma; the mean survival time was 9 days. Thus, a strong though presumptive diagnosis of brain death may be made in those patients with absent electrical activity on the CFM and evidence of absent brain stem, i.e., respiratory center, function.