OBJECTIVE To study the efficacy of combined use of low-dose granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in mobilizing hematopoietic stem/progenitor cells. METHODS Twenty adult patients with malignant hematologic diseases were paired using statistical methods, and the 10 pairs were divided into 2 equal groups. For non-Hodgkin lymphoma, the treatment regimen adopted intravenous infusion of cytoxan (2 g/d for 1 or 2 d) and VP16 (0.2 g/d for 1 to 3 d), while for acute non-lymphocytic leukemia, Ara-C (2 g/d for 1 to 3 d) and VP16 (0.2 g/d for 1 to 3 d) were used. When the while blood cell count (WBC) was below 1.0 x10(9)/L, G-CSF and GM-CSF were administered subcutaneously at the same dose of 2.5 microg/d.kg in the 10 patients in the experimental group, while the patients in the control group received only 5 microg/d.kg G-CSF, both for 5 to 6 d. After WBC>5.0 x 10(9)/L, the peripheral blood mononuclear cells (PBMNC) were separated by CS-3000 pluse separator and CD34+ cells were determined by flow cytometry. RESULTS The purity of the isolated PBMNC was 95%-99%. In the experimental group, the mean number of CD34+ cells acquired was 9.4 x 10(6)/kg ranging from 8.4 x 10(6) to 10.2 x 10(6)/kg, and granulocyte-macrophage colony-forming unit (CFU-GM) was 42.4 x 10(4)/kg on average ranging from 21.9 x 10(4) to 72.8 x 10(4)/kg, as compared with 4.8 x 10(6)/kg [(4.1-8.3) x10(6)/kg] for CD34+ cells and 28.1 x 10(4)/kg [(7.1-60.2) x 10(4)/kg] for CFU-GM in the control group (P<0.05). No obvious difference was observed between the two groups in terms of the adverse effects of the treatment (P>0.05). CONCLUSIONS Combined use of G-CSF and GM-CSF can be more effective than the exclusive use of GM-CSF for mobilizing CD34+ cells.