A case is presented that suggests that intrauterine transfusion carries the risk of sensitization to red cell antigens other than Rh0+In this case intrauterine transfusions of Jk11positive red cells were followed by the appearance in the mother's serum of anti-Jk, an antibody known to cause hemolytic disease of the newborn. The use of the mother as a donor of red cells for her fetus will circumvent the problem of further maternal sensitization.