Four patients with acute myeloid leukaemia relapsed within 6 months of allogeneic BMT. Three patients were treated with cytosine arabinoside and amsacrine while the fourth received no chemotherapy. All patients received infusions of leucocytes obtained by repeated leukapheresis from the original bone marrow donor. Three patients developed GVHD requiring immunosuppressive therapy. One of these achieved a complete remission which has been sustained for more than 1 year with 100% donor haematopoiesis. The other patients died with persistent leukaemia 45-134 days after the infusions of donor cells. We conclude that the addition of marrow donor leucocytes to salvage chemotherapy may produce durable remissions in patients with acute myeloid leukaemia relapsing after BMT and that this may be due to a graft-versus-leukaemia effect.