A 74-year-old woman was scheduled for total arch replacement because of an enlarging thoracic aortic aneurysm in the aortic arch. Her preoperative blood test showed an elevated cold agglutinin with a titre of 2,048. There was concern about hemagglutination during hypothermia and hemolysis when returning to natural temperature under hypothermic circulatory arrest. We usually use moderate hypothermia (a minimum rectal temperature of 27℃) with circulatory arrest during total arch replacement. A cooling test was performed with her blood, which found no coagulation reaction in vitro at 25℃. There was a possibility that the total arch replacement would be carried out under moderate hypothermia, but it was by no means certain. After discussing the case with the hematologist, anesthetist, and clinical engineer, we decided on a minimum temperature of 30℃ during circulatory arrest because hemagglutination or hemolysis can become an issue in cardiopulmonary bypass. Coronary perfusion was maintained by infusing blood cardioplegia at 30℃ every 30 min. The intra-aortic occlusion balloon was inflated in the descending aorta, and perfusion of the spinal cord and lower body was initiated via the left femoral artery during circulatory arrest. Total selective cerebral perfusion flow was maintained at 1.5 times normal (20 ml/kg/min). There was no hemagglutination or hemolysis during the operation and no neurological complications in the postoperative period. For patients with cold agglutinin, individual cardiopulmonary bypass planning is necessary, depending on the severity of the condition and operative method.