Recommendations for the optimal transfusion support of patients likely to receive repeated platelet transfusions. 1. Determine policy for prophylactic platelet support, and select the platelet count below which platelet transfusions will be used. 2. Consider using leucocyte depletion of red cell and platelet concentrates to prevent HLA alloimmunization from the outset. 3. Type patients for HLA-A and B antigens at an early stage. 4. Use random donor platelet concentrates for initial platelet support (either single or multiple donor, depending on availability). 5. If refractoriness occurs, determine whether clinical factors, which may be associated with non-immune consumption of platelets, are present and test the patient's serum for HLA antibodies. 6. Use HLA-matched platelet transfusions if HLA alloimmunization is the most likely cause of refractoriness. 7. If there is no improvement with HLA-matched transfusions, platelet crossmatching may identify the cause of the problem and help with the selection of compatible donors. 8. Discontinue prophylactic platelet support if a compatible donor cannot be found. Use platelet transfusions from random donors to control bleeding and increase the dose, if necessary.