Based on the findings in a collaborative study of 503 comatose and apneic patients, the establishment of cerebral death requires (1) that all appropriate examinations and therapeutic procedures have been performed, (2) that cerebral unresponsivity, apnea, dilated pupils, absent cephalic reflexes, and electrocerebral silence be present for 30 minutes at least six hours after the ictus, and (3) that if one of these standards is met imprecisely or cannot be tested, a confirmatory test be made to demonstrate the absence of cerebral blood flow. This would allow the diagnosis of a dead brain to be made in patients with small amounts of sedative drugs in the blood, in patients undergoing therapeutic procedures that make examination of one or more of the cranial nerves impossible, and in patients otherwise meeting the criteria whose pupils are small. (JAMA237:982-986, 1977)