Objective To observe the antileukemic effect in relap se patient s by infusion of donor mmunocompetent cells with or without granulocyte colony2stimulating factor(G2CSF) mobilization. Methods Twenty patient s with leukemia in relap se after allogeneic bone marrow transplantation(allo2BMT) were treated with chemotherapy followed by donor2derived lymphocyte s(DDL) without G2CSFmobilization(Group A, n=11), or donor peripheral blood progenitor cells(PBPCs ) with G2CSF mobilization(Group B, n=9). Results Five patient s in Group A were in hematologic relap se. After DDL infusion, 3 of 5 patient s had a temporary complete remission(CR) and relap sed after3, 7 and 10 months, re spectively. One achieved partial remission and died of interstitial pneumonia; and the other one showed no re sponse. Another 6 patient s in Group A were in cytogenetic relap se or central nerve system(CNS) leukemia, and all achieved CR and remained in disea se free survival(DFS) for 10 to 98 months after DDL infusion. All 9 patient s in group B were in hematologic relap se. Three patient s with chronic myeloid leukemia (CML) had cytogenetic and molecular remission for 16, 35 and 51 months, re spectively after PBPC infusion; and 5 patient s with acute lymphoid leukemia(ALL) had CR and were still in CR for 10 to 18 months except 1 patient relap sed soon. And the other one with AML showed no re sponse to the therapy. Conclusion Donor immunocompetent cells infusion is an effective therapy for relap sed leukemia after allo2 BMT, e specially for the patient s with early(molecular and cytogenetic) or CNS relapse. Infusion of donor PBPC mobilized by G2CSF seems to have more potentiated graft2versus2leukemia(GVL) effect than DDL