In 54 patients with circulatory arrest mainly due to ischaemic heart disease cerebral functions were tested longitudinally during primary cardiopulmonary resuscitation or basic life support. Cerebral recovery was characterized by the appearance of functions in caudorostral sequence. Cerebral prognosis was reliably assessed by the time to reappearance of respiratory movements, pupillary light, coughing--swallowing and ciliospinal reflexes, as these were regained within critical time limits of 7, 12, 23 and 26 min respectively, corresponding to the longest delay compatible with recovery of consciousness and within ultimate time limits of 15, 28, 58 and 52 min corresponding to the longest delay compatible with any cerebral recovery at all. Prognostication was currently ascertained during basic life support as reflex reappearance times were exponentially interdependent. If circulation was re-established it usually happened within less than 20 min of basic life support. Prolongation of the resuscitation attempt beyond this time occasionally resulted in a selective reestablishment of circulation (brain death) but most often resulted in a dissociated recovery of cerebral functions (cardiac death).