A method is described to purify murine hematopoietic stem cells. The procedure involves fluorescence-activated cell sorting of nonadherent nucleated bone marrow cells for the presence of the antigen, Thy1.2, and the absence of the lineage-specific antigens, Lyt2, L3T4, Mac1, B220, and J11D.2. These Thy1.2+T-B-M-J- cells are 200-800-fold enriched in in vitro colony-forming units. Moreover, this narrow subset shows enhanced ability to form spleen colonies and engraft lethally irradiated mice. Data reported herein demonstrate that these purified pluripotent stem cell populations also have enhanced potential for the rescue of lethally irradiated haplotype-mismatched mice.