There is reported about the treatment of refractory thrombocytopenia in a 9 years old boy following the autologous bone marrow transplantation for acute lymphoblastic leukaemia. The megakaryocytes were found diminished in the bone marrow smears. Controls of the thrombocyte count and the kinetics with radioactively labeled platelets of a donor spoke in favour of immunothrombocytopenia. Threatening bleeding complications challenged the use of all treatment possibilities. The irradiation of the spleen was without any success. After the splenectomy the thrombocyte count increased slowly, but after a remarkable lag phase, however. A diminished reproduction capacity of the bone marrow graft for special cell sorts has to be taken into account in such cases. The usual cytodynamics after splenectomy cannot be expected at all.