Development of permanent platelet refractoriness is a major problem in multitransfused patients with diseases such as leukemia, aplastic anemia, or pediatric solid tumors. We tried to prevent alloimmunization in these patients by systematic use of leukocyte-free blood components with less than one million of contaminating leukocytes per unit of platelets or red cells. Our study group comprised 26 patients with a minimum of 10 platelet transfusions per patient. These patients were compared with a historical reference group of 21 patients who had received standard blood products. In the leukocyte-free group none developed platelet refractoriness, in contrast to the reference group where 11 of the 21 patients became refractory to random platelets. The median corrected platelet increment for random pooled platelets was significantly higher in the leukocyte-free group compared with the reference group. The increasing number of transfusions did not correlate with the development of platelet refractoriness; instead we propose that the lower limit of antigenic exposure is important. We conclude that systematic use of leukocyte-free blood components effectively prevents development of platelet refractoriness and contributes to optimal supportive care of children with cancer.