Two patients affected by acute leukemia relapsed 10 and 12 months respectively after allogeneic bone marrow transplantation. They were treated with aggressive chemotherapy and then infused with HLA-identical donor leukocytes (DLI) collected after recombinant human granulocyte colony-stimulating factor (rhG-CSF) administration. A total of 5.6 and 6.3 x 10(6)/kg CD34+ cells, 2.7 and 3.0 x 10(4)/kg CFU-GM, 4.7 and 4.4 x 10(8)/kg MNC, 4.6 and 3.9 x 10(9)/kg PMN respectively were infused. Both patients achieved complete remission (CR) and complete chimerism was re-established. One patient developed grade IV acute graft-versus-host disease of the liver requiring immunosuppression and he died in CR from disseminated aspergillosis, 7 months after chemotherapy; one patient is alive in relapse 12 months after treatment.