Myeloablative treatment followed by allogeneic transplantation of peripheral blood hemopoietic progenitors (alloPBT) was administered to five leukemia patients with a high risk of relapse. The donors subcutaneously received 10 micrograms/kg/day of G-CSF for five days. The tolerance to this medication was good with only complaints of moderate bone pain. Two of the peripheral blood donors had previously been bone marrow donors and both expressed their preference for the new method. The product of peripheral blood leukapheresis contained from one to four-fold more hemopoietic progenitors and approximately ten-fold more T-lymphocytes than the bone marrow received from normal donors. Prophylaxis of the graft versus host disease (GVHD) consisted of cyclosporine A (CsA) in one case and CsA and methotrexate (MTX) in four cases. The bone marrow implantation was verified with a neutrophil count of up to more than 0.5 x 10(9)/l between days 12 to 21 after transplant and a platelet count higher than 20 x 10(9)/l from days 11 to 41 after transplant. Acute GVHD was clinical grade O (two cases), II (one case) and grade III (two cases). In conclusion, alloPBT may be more safely and comfortably performed to the donor. This method may provide rapid recovery of neutrophils and platelets in patients without an apparent increase in the risk of developing graft versus host disease.