Objective To observe the antileukemic effect in relapse patients by infusion of donor immunocompetent cells with or without granulocyte colony-stimulating factor (G-CSF) mobilization.Methods Twenty patients with leukemia in relapse after allogeneic bone marrow transplantation (allo-BMT) were treated with chemotherapy followed by donor-derived lymphocytes (DDL) without G-CSF mobilization (Group A, n=11), or donor peripheral blood progenitor cells (PBPCs) with G-CSF mobilization (Group B, n=9).Results Five patients in Group A were in hematologic relapse. After DDL infusion, 3 of 5 patients had a temporary complete remission (CR) and relapsed after 3, 7 and 10 months, respectively. One achieved partial remission and died of interstitial pneumonia; and the other one showed no response. Another 6 patients in Group A were in cytogenetic relapse or central nerve system (CNS) leukemia, and all achieved CR and remained in disease free survival (DFS) for 10 to 98 months after DDL infusion. All 9 patients in group B were in hematologic relapse. Three patients with chronic myeloid leukemia (CML) had cytogenetic and molecular remission for 16, 35 and 51 months, respectively after PBPC infusion; and 5 patients with acute lymphoid leukemia (ALL) had CR and were still in CR for 10 to 18 months except 1 patient relapsed soon. And the other one with AML showed no response to the therapy.Conclusion Donor immunocompetent cells infusion is an effective therapy for relapsed leukemia after allo-BMT, especially for the patients with early (molecular and cytogenetic) or CNS relapse. Infusion of donor PBPC mobilized by G-CSF seems to have more potentiated graft-versus-leukemia (GVL) effect than DDL infusion.