Allogeneic bone marrow transplantation is an accepted therapy for acute leukemia, with an increased rate of long-term survival and possible cure. Unfortunately, it can be given only when an HLA-identical donor is found. For this reason, large international registries containing normal HLA-typed volunteer marrow donors have been established. Although preliminary, results are encouraging. Approaches using stem cell purification and expansion, fetal and neonatal cells, and new immunosuppressive agents are currently under investigation.