In this randomized prospective study, we included 30 patients with different hematological diseases (acute myeloid leukemia, acute lymphoblastic leukemia, chronic myeloid leukemia, myelodysplastic syndrome or severe aplastic anemia) to compare peripheral blood stem cells (PBSC) (15 patients; mean age 23) and bone marrow (BM) (15 patients; mean age 21.8) as a source for allogeneic transplantation regarding the tempo of hematopoietic recovery and the incidence of acute graft-versus-host disease (GVHD). In the BM group, the median nucleated cell count harvested was 1.3 x 10(10), while in the PBSC group, the aphereses contained a median of 4.4 x 10(6) CD34+/kg recipient weight. PBSC transplantation (PBSCT) was associated with faster hematopoietic reconstitution measured as absolute neutrophil count (ANC) >0.5 x 10(9)/l (log-rank P value <0.0018) and platelet count >25 x 10(9)/l (log-rank P value <0.0098). Seven patients (46.7%) in the BM group vs only one patient (6.7%) in the PBSC group developed acute GVHD (P = 0.013). Therefore, we conclude that PBSCT is associated with faster hematopoietic recovery and the incidence of acute GVHD does not exceed that seen with BMT.