About 2 or 3 weeks after transplantation, even ABO-Incompatible bone marrow shows a successful graft. Haemopoiesis is not always free of problems. Suppression of erythropoiesis is caused by persistently incompatible agglutinins. Patient's well-being is limited by longer periods of low levels of haemoglobin concentration. Long-lasting need for transfusions is related to the well-known risk of infections. A procedure to eliminate the residual titers of alloantibodies should be discussed in time with the staff of the transfusion department.