A 3-year-old girl with BCR/ABL-positive CML relapsed after related HLA-identical cord blood transplantation. She was treated with three cycles of donor lymphocyte (DLI) infusion from her 15-month-old brother. Interferon alpha was added after the second DLI, whereas a trial of IL-2 had to be discontinued because of increasing immature myeloid cells in the blood smear. No signs of GVHD were observed, but she developed myelosuppression and needed one platelet and one red blood cell transfusion. She achieved a molecular remission after 6 months with transient molecular relapse followed by sustained remission for 15 months. Thus, DLI with or without interferon alpha might prove to be a promising treatment option with tolerable side-effects in relapsed CML after cord blood transplantation. Bone Marrow Transplantation (2000) 25, 219-222.