The role of recombinant human granulocyte colony-stimulating factor (rHuG-CSF) in myeloid recovery of children given an allogeneic bone marrow transplant (BMT) from an HLA-identical sibling for acute leukemia was evaluated in a retrospectively historically controlled study, involving 20 consecutive treated patients and 30 historical controls. In order to investigate the efficacy of rHuG-CSF in patients given a matched unrelated BMT with methotrexate as part of graft-versus-host disease (GVHD) prophylaxis, we also analyzed the kinetics of engraftment in eight further children with acute or chronic leukemia, transplanted using a volunteer donor. Patients were treated with 5 micrograms/kg/day of rHuG-CSF by 1-h intravenous infusion from day +5 until the absolute neutrophil count (ANC) was > or = 2 x 10(9)/l. No adverse effect related to treatment was observed in any patients. Children transplanted from an HLA-identical sibling and treated with rHuG-CSF reached an ANC count greater than 0.5 x 10(9)/l, 1 x 10(9)/l and of 2 x 10(9)/l in a significantly shorter time than the control group (day +9, +10 and +12, vs day +15, +22 and +29, respectively). An accelerated granulocyte production was also observed in patients receiving an unrelated transplant after a GVHD prophylaxis schedule including methotrexate, the median time to neutrophil recovery above 0.5 x 10(9)/l, 1 x 10(9)/l and 2 x 10(9)/l being +14, +15 and +17 days, respectively. In comparison to historical controls, all rHuG-CSF-treated patients had fewer days of fever, of antibiotic therapy and, only for children with HLA-compatible siblings, of hospitalization, whereas in the three groups the duration and severity of mucositis were comparable. No difference between the rHuG-CSF-treated patients and the historical controls given BMT from HLA-identical sibling was seen with regard to incidence of acute or chronic GVHD, relapse rate and actuarial event-free survival at day +100 and 1 year after transplantation. Our data suggest that in children given allogeneic BMT for acute or chronic leukemia, rHuG-CSF reduces duration of neutropenia, without increasing the rate of relapse or the incidence and severity of GVHD.