THE ADVENT of effective artificial cardiopulmonary support for severely brain-injured persons has created some confusion during the past several decades about the determination of death. Previously, loss of heart and lung functions was an easily observable and sufficient basis for diagnosing death, whether the initial failure occurred in the brain, the heart and lungs, or elsewhere in the body. Irre-For editorial comment see p 2194. versible failure of either the heart and lungs or the brain precluded the continued functioning of the other. Now, however, circulation and respiration can be maintained by means of a mechanical respirator and other medical interventions, despite a loss of all brain functions. In these circumstances, we recognize as dead an individual whose loss of brain functions is complete and irreversible. To recognize reliably that death has occurred, accurate criteria must be available for physicians' use. These now fall into two groups, to be applied