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T he mechanisms of BM hematopoietic stem/progenitor cell (HSPC) adhesion, engraftment, and mobilization remain incompletely identified. Here, using WT and transgenic mice, we have shown that membrane-anchored plasminogen activator, urokinase receptor (^MuPAR) marks a subset of HSPCs and promotes the preservation of the size of this pool of cells in the BM. Loss or inhibition of ^MuPAR increased HSPC proliferation and impaired their homing, engraftment, and adhesion to the BM microenvironment. During mobilization, ^MuPAR was inactivated by plasmin via proteolytic cleavage. Cell-autonomous loss of the gene encoding ^MuPAR also impaired long-term engraftment and multilineage repopulation in primary and secondary recipient mice. These findings identify ^MuPAR and plasmin as regulators of the proliferation, marrow pool size, homing, engraftment, and mobilization of HSPCs and possibly also of HSCs.