Improvements in the availability and quality of platelet transfusions have markedly reduced the morbidity and mortality associated with intensive myelosuppressive therapy. Alloimmunization and refractoriness to platelet transfusion remains a significant clinical problem, although the incidence of alloimmunization may be declining due to more widespread use of leucocyte depleted products. Alloimmunization can be distinguished from other causes of poor post transfusion increments by the measurement of lymphocytotoxic or antiplatelet antibodies. In addition to medical approaches to reduce the risk of bleeding in individual patients, identification of histocompatible donors can usually be accomplished by HLA matching of donor and recipient, platelet cross matching or a combination of both techniques. There are a number of selection strategies which can be utilized and optimal patient management requires close cooperation and communication between clinicians and blood centers.