Hematopoietic growth factors have been shown to be effective in reducing the period of neutropenia after autologous bone marrow transplantation (BMT). Initial concerns over potential aggravation of graft-versus-host disease (GVHD) and increase in the incidence of relapse in patients with myeloid leukemias influenced the number of studies using hematopoietic growth factors after allogeneic BMT. We report the experience with 50 patients treated at a single institution using granulocyte colony-stimulating factor (G-CSF) after allogeneic sibling (n = 30) and matched unrelated (n = 20) BMT. The time to an absolute neutrophil count > or = 500/microL was significantly faster in patients who received G-CSF and cyclosporine and prednisone for GVHD prophylaxis when compared with historical control patients receiving the same GVHD prophylaxis (10 v 13 days, P < .01). A similar accelerated myeloid engraftment was observed for those patients who received the addition of methotrexate for GVHD prophylaxis when compared with historical control patients receiving the same GVHD prophylaxis regimen (16 v 19 days, P < .05). The median time to engraftment for patients receiving a matched unrelated BMT and G-CSF was 17 days (range 13 to 26). We did not observe any increase in GVHD or early mortality in the matched related sibling BMT. The incidence of acute GVHD in the matched unrelated BMT recipients was also low at 21%; however, 9 patients (45%) died within 100 days of the date of BMT, similar to the experience reported with granulocyte-macrophage CSF. This study confirms the efficacy of G-CSF in accelerating myeloid engraftment after allogeneic matched sibling BMT. The higher early mortality associated with patients receiving matched unrelated BMT suggests that randomized controlled trials using G-CSF after allogeneic BMT should be performed.