Sixteen patients with severe thrombocytopenia and secondary bone marrow inhibition were given 81 thrombocyte concentrates. In 55.6% platelet transfusions led to an adequate posttransfusion rise of platelets, in 44.4% of thrombocyte transfusions the increase of platelets was not satisfactory. The cause of the inadequate posttransfusion rise of platelets in 19.4% were antibodies against HLA antigens. In addition to other known factors which influence the rise of platelets a significant relationship was revealed between administration of Amphotericin B, broad spectrum bactericide antibiotics and the body temperature. To improve substitution of thrombopenic patients by platelet concentrates the authors recommend to create a national register of HLA typed donors.