Autologous bone marrow transplantation (ABMT) is the treatment of choice for selected patients with acute myelogenous leukemia, non-Hodgkin's lymphoma, and poor prognosis breast cancer. A possible limitation of this approach is that clonogenic tumor cells could be collected and infused back into the patient along with the normal bone marrow. The major emphasis in our laboratory has been the development of marrow purging regimens for breast cancer patients. This paper describes two investigative approaches hematopoietic progenitor cell protection and selection. We describe how the use of G-CSF in the patients who receive positively selected marrow shortens the rate of engraftment.