Prospective studies have shown rapid engraftment using granulocyte-colony-stimulating factor-mobilized peripheral blood stem cells (G-PBSCs) for allogeneic transplantation, though the risks for graft-versus-host disease (GVHD) may be increased. It was hypothesized that the use of G-CSF to prime bone marrow (G-BM) would allow rapid engraftment without increased risk for GVHD compared with G-PBSC. Patients were randomized to receive G-BM or G-PBSCs for allogeneic stem cell transplantation. The study was designed (beta <.8) to detect a difference in the incidence of chronic GVHD of 33% (alpha <.05). The plan was to recruit 100 patients and to conduct an interim analysis when the 6-month follow-up point was reached for the first 50 patients. Fifty-seven consecutive patients were recruited (G-BM, n = 28; G-PBSC, n = 29). Patients in the G-PBSC group received 3-fold more CD34(+) and 9-fold more CD3(+) cells. Median times to neutrophil (G-BM, 16 days; G-PBSC, 14 days; P <.1) and platelet engraftment (G-BM, 14 days; G-PBSC, 12 days; P <.1) were similar. The use of G-PBSC was associated with steroid refractory acute GVHD (G-BM, 0%; G-PBSC, 32%; P <.001), chronic GVHD (G-BM, 22%; G-PBSC, 80%; P <.02), and prolonged requirement for immunosuppressive therapy (G-BM, 173 days; G-PBSC, 680 days; P <.009). Survival was similar for the 2 groups. Compared with G-PBSC, the use of G-BM resulted in comparable engraftment, reduced severity of acute GVHD, and less subsequent chronic GVHD.