A 43-year-old man with chronic myeloid leukaemia underwent a second transplant with CD34+ bone marrow cells selected from his two-loci HLA-mismatched sibling after rejection of the first graft from an HLA-matched unrelated donor. By immunomagnetic positive selection, CD34+ marrow cells at 0.95 x 10(6)/kg with 97% purity and CD3+ T lymphocytes at 1.3 x 10(4)/kg were collected and transplanted. Engraftment was confirmed to be of CD34+ cell-donor origin. The patient developed only grade I acute graft-versus-host disease (GVHD) and no chronic GVHD to date. These observations suggest that allogeneic CD34+ bone marrow cells are capable of reconstituting haemopoiesis and that CD34+ selection could be applicable to T-cell depletion.