Abstract.Bone marrow transplant recipients at Huddinge Hospital have routinely received single‐donor platelet concentrates (PC) from blood group 0 donors. These PC contain approximately 350 ml plasma, which is incompatible with patients of group A, B and AB. In 27 patients transplanted with an ABO‐identical bone marrow, serological investigations have been performed every week after transplantation (median 6 weeks, range 3–14). Nine of 11 recipients with blood group A developed a positive direct antiglobulin test (DAT) after PC transfusions, while none of 15 patients of blood group 0 developed a positive DAT. Anti‐A could be eluted in DAT‐positive cases. In no case was there any clinical sign of hemolysis. Nor did recipients of groups A, B or AB (n = 34) require more red blood cells or PC transfusions compared to recipients of group 0