Profound hypothermia associated with circulatory arrest is the commonest method of cerebral protection during operations on the aortic arch. This technique allows a limited time to perform the aortic repair, however. It also necessitates prolonged cardiopulmonary bypass to rewarm the patient. This may be the cause of coagulation disorders or infection. Selective perfusion of the carotid arteries can also be used. When the perfusion is derived from the main arterial line, however, the repair of the aorta requires that the vessel be crossclamped, and cannot be performed in an "open, bloodless" manner. To avoid the disadvantages of both techniques, we have developed a new technique of cerebral protection. After a regular cardiopulmonary bypass has been established, the carotid arteries are cannulated and perfused with blood cooled at 6 degrees to 12 degrees C, through a separate heat exchanger, while the core temperature is maintained at moderate hypothermia (25 degrees to 28 degrees C, rectal). To perform the "open" distal repair, the cardiopulmonary bypass is discontinued while the carotid perfusion is maintained (250 to 350 ml/min). When the distal repair is completed, cardiopulmonary bypass is resumed and the carotid perfusion is discontinued. Between 1984 and June 1989, 54 patients (mean age 55 years) were operated on with this method (45 elective operations, 9 emergency procedures). Mean duration of cardiopulmonary bypass was 121 minutes (65 to 248), and mean duration of circulatory arrest was 22 minutes (10 to 51). The electroencephalogram, routinely recorded, showed return of the cerebral activity after a mean time of 12 minutes and normal activity after a mean time of 66 minutes. There was no intraoperative death. Hospital mortality rate was 13% (7/54). One death was related to neurologic disorders. All patients but one awakened normally within 8 hours after operation. Two patients (4.3%) experienced a transient neurologic episode (lateral hemianopia) 9 and 11 days postoperatively. There was no hemorrhagic complication (24-hour average blood loss: 840 +/- 540 ml). In our experience the technique of "cold cerebroplegia" has been demonstrated to provide excellent cerebral protection. It requires no prolonged cardiopulmonary bypass and does not limit the time necessary to perform the aortic repair. It may be considered as a safe alternative to profound hypothermia associated with circulatory arrest.