Transfusion refractoriness to platelets is characterized by an inadequate increment in the posttransfusion platelet count and/or reduced haemostatic effect following platelet transfusion. As a consequence of more intensive bone marrow toxic therapeutic approaches there is an increased use of platelet transfusion, and the refractory state is encountered in about half of young patients treated for haematological malignancies. The acquired condition is mainly due to alloimmunization against HLA-antigen on leucocytes in the transfused platelets or to non-immunological factors, e.g. fever, infections, bleedings, antibodies or splenomegaly. Profylactic reduction of the leucocyte content by filtration of transfusion products diminishes the risk of alloimmunization and the refractory state. Treatment of the refractory state is bleeding is transfusion with HLA-compatible platelets or large amounts of platelet concentrates. Splenectomy and treatment with steroids or intravenous gammaglobulin have been unsuccessful. Recently a new haematopoietic growth factor, thromapoietin, which regulates megakaryocytopoiesis has been identified. In the near future such a recombinant human growth factor will most likely reduce the need for platelet transfusion and its side effects.