Aprotinin, a proteinase inhibitor, is known to significantly reduce blood loss during cardiac, thoracic and vascular surgery. Despite the wide use of this medication, there are only a few reports of anaphylactic reactions. We experienced a case of severe intraoperative anaphylactic reaction due to reexposure of aprotinin used to reduce intraoperative bleeding. During anesthesia for brain tumor removal, systemic hypotension and generalized rash were developed following the administration of aprotinin in a 34-year-old woman. We suggest that it is necessary, in patients known to have had previous aprotinin therapy, to perform skin test with diluted aprotinin before infusion.