The Blood and Marrow Transplant Clinical Trials Network conducted 2 parallel multicenter phase 2 trials for individuals with leukemia or lymphoma and no suitable related donor. Reduced intensity conditioning (RIC) was used with either unrelated double umbilical cord blood (dUCB) or HLA-haploidentical related donor bone marrow (Haplo-marrow) transplantation. For both trials, the transplantation conditioning regimen incorporated cyclophosphamide, fludarabine, and 200 cGy of total body irradiation. The 1-year probabilities of overall and progression-free survival were 54% and 46%, respectively, after dUCB transplantation (n = 50) and 62% and 48%, respectively, after Haplo-marrow transplantation (n = 50). The day +56 cumulative incidence of neutrophil recovery was 94% after dUCB and 96% after Haplo-marrow transplantation. The 100-day cumulative incidence of grade II-IV acute GVHD was 40% after dUCB and 32% after Haplo-marrow transplantation. The 1-year cumulative incidences of non-relapse mortality and relapse after dUCB transplantation were 24% and 31%, respectively, with corresponding results of 7% and 45%, respectively, after Haplo-marrow transplantation. These multi-center studies confirm the utility of dUCB and Haplo-marrow as alternative donor sources and set the stage for a multi-center randomized clinical trial to assess the relative efficacy of these 2 strategies. The trials are registered at www.clinical-trials.gov under NCT00864227 (BMT CTN 0604) and NCT00849147 (BMT CTN 0603).