Auditory evoked brain-stem responses (ABRs) were recorded in 19 out of 52 brain dead cases in Department of Emergency Medicine, University of Tokyo Hospital from May, 1981 to January, 1984. The causes of brain death were severe head injury (9 cases), cerebro-vascular disease (7 cases), anoxia (2 cases), hydrocephalus (1 case). Eleven cases of them fulfilled the clinical criteria which included absence of cortical and brain-stem functions excluding severe hypothermia and depressant drug intoxication. The remainders who were subjected to barbiturate therapy were diagnosed as brain death for non-filling phenomenon in cerebral angiography. Results were as follows; Fourteen cases (74%) had no identifiable ABR waves. One case (5%) had only 1st wave. Three cases (16%) had 1st and 2nd waves. One case (5%) had 1st, 2nd, and 3rd waves. In spite of definition of clinical brain death, 5 cases had at least 1st wave, and therefore these datum suggested that ABR might have less clinical utility in diagnosis of brain death. Each case did not necessarily demonstrate the total extinction of ABRs, as was shown in (2) to (4) mentioned above. The clinical status which met the criteria of brain death might therefore possibly imply any conditions in which brain death was impending gradually to result in the total brain death of cerebrum through medulla oblongata. Under these circumstances, how barbiturate might produce ABRs abnormality remained unsolved, though it has been said not to produce ABRs abnormality. Among 8 cases under barbiturate therapy, there were 5 cases with no identifiable waves and 3 cases with 1st and 2 nd waves.(ABSTRACT TRUNCATED AT 250 WORDS)