IN 1994, APPROXIMATELY 500,000 patients in the United States underwent cardiac surgery employing cardiopulmonary bypass.1 Cardiopulmonary bypass is associated with deleterious effects on platelet number and function, leading to excessive bleeding in 5% to 25% of patients.2,3 About half of the 7 million units of platelets transfused annually in the United States are to patients undergoing cardiac surgery, most of which are administered by anesthesiologists.4 The American Society of Anesthesiologists (ASA) guidelines for platelet administration are outlined in Table 1. Because of the widespread use of platelet transfusions, many adverse effects have been recognized. In this review, the incidence, cause, and currently available treatment modalities to treat febrile reactions after platelet transfusions are discussed. In particular, attention is focused on the importance of bacterial contamination of platelets, a rare but potentially fatal complication.