The routine use of platelet concentrates has greatly increased during the last years. Most of the concentrates are transfused to hematologic patients, who frequently receive additional red blood cells. These polytransfusion regimens often result in the formation of HLA- or platelet-specific antibodies, which lead to refractoriness to further platelet support. In order to avoid this problem, the number of HLA antigens transmitted should be reduced. Therefore, a consequent leukocyte depletion of all blood products administered to multitransfused patients seems to be necessary. If antibodies are already preformed in the patient's serum, compatible platelets have to be selected for transfusion.