Autologous bone marrow transplantation for leukemia was developed to extend the apparent curative potential of myeloablative therapy with allogeneic bone marrow transplantation to leukemia patients without histocompatible marrow donors. The conceptual problem with this approach is obvious: if the need for the transplant is based on overt or occult contamination of the marrow by leukemia, the use of autologous marrow seems destined to failure because of reinfusion of leukemia cells along with the harvested marrow. For this reason, ex vivo antileukemic treatment ("purging") of remission marrow was developed to justify autologous transplants for leukemia. Clinical trials involving thousands of patients worldwide have demonstrated curative potential of autologous bone marrow transplants, using purged or untreated remission marrow, for selected patients with acute myelogenous leukemia and acute lymphocytic leukemia. Purging appears to contribute to increased leukemia-free survival, at least in a subset of patients who are at very high risk of relapse, but this has not been tested in a prospective randomized trial and remains controversial. In acute myelogenous leukemia, in which the greatest experience exists, procedure-related mortality is much less for autologous than for allogeneic transplants; however, since leukemia relapse is much more frequent for autologous than for allogeneic transplants, the long-term disease-free survival is similar. In general, autologous transplants are preferred for older individuals and those without matched related donors, whereas allogeneic transplants are preferred for younger patients with matched related donors. Leukemia relapse has greatly limited the success of autologous transplants for acute lymphocytic leukemia. Autologous transplants for the chronic leukemias are in a much earlier stage of investigation. Autologous transplantation for leukemia is a fertile area for research. Important topics include conditioning regimens with improved antileukemic efficacy, the value of purging and the best method(s) for leukemia stem cell purging or normal stem cell selection, the possibility of inducing an autologous graft versus leukemia reaction, the use of immunomodulatory cytokines for postgrafting immune system manipulation, and the use of hematopoietic growth factors for ex vivo stem cell expansion and postgrafting support of marrow recovery.