Anaphylactic reactions to colloid volume substitutes, such as dextran, are rare, however, with their increasing utilization in clinical practice an increasing awareness of their potential antigenicity is required. This article reports a severe allergic reaction induced by infusion of dextran 40 during the beginning of a general anesthesia in a 59 year old patient who was going to be submitted to an operation for treatment of chagasic megacolon. The patient died from this complication after 28 days. A review of literature of this complication and a discussion about its physiopathological mechanism and prevention is presented.