A 64-year-old patient with factor IX deficiency (Christmas disease) underwent quadruple coronary bypass grafting for angina pectoris. Excessive bleeding was prevented by infusion of factor IX concentrates from one day before surgery until the 19th postoperative day. The surgical procedure and the cardiopulmonary bypass were carried out in the same manner as in patients without any haemorrhagic disorder. No haemorrhagic complication occurred, neither during nor after the operation.