Transplanted HSCs engraft into unconditioned bone marrow without HSC replacement. The chimerism in phenotypic HSCs (CD34⁻CD150⁺CD48⁻LSK) (A) and number of donor (CD45.2⁺) phenotypic HSCs (B) in the bone marrow of unconditioned CD45.1 × CD45.2 recipients 13 to 16 weeks after the transplantation of 2500 to 2.5 × 10⁵ purified CD45.2 HSCs (n = 14). The numbers of donor (CD45.2⁺), endogenous (CD45.1⁺CD45.2⁺), and total phenotypic HSCs (C) and functional HSCs (D-E) in untransplanted mice or unconditioned mice transplanted with 2.5 × 10⁵ purified HSCs (C-D) (n = 3) or 6.5 × 10⁸ purified Lin⁻ cells (E) (n = 4). Functional HSCs were estimated using repopulating units (RUs) (D-E). The chimerism in phenotypic HSCs, GMPs, and CLPs in the bone marrow (BM), and Gr-1^hi granulocytes, B220^hi B cells, and CD3⁺ T cells in the peripheral blood (PB) of unconditioned recipients 13 weeks after the transplantation of 2.5 × 10⁵ HSCs (F) (n = 3). All error bars represent standard deviations of the means. *P < .05.