Flt3 has emerged as a potential regulator of hematopoietic stem cells (HSC). Sixty percent of cells in the mouse marrow Lin⁻Sca1⁺c-kit⁺ HSC pool expressed flt3. Although single cell cloning showed comparable high proliferative, myeloid, B, and T cell potentials of Lin⁻Sca1⁺c-kit⁺flt3⁺ and Lin⁻Sca1⁺c-kit⁺flt3⁻ cells, only Lin⁻Sca1⁺c-kit⁺flt3⁻ cells supported sustained multilineage reconstitution. In striking contrast, Lin⁻Sca1⁺c-kit⁺flt3⁺ cells rapidly and efficiently reconstituted B and T lymphopoiesis, whereas myeloid reconstitution was exclusively short term. Unlike c-kit, activation of flt3 failed to support survival of HSC, whereas only flt3 mediated survival of Lin⁻Sca1⁺c-kit⁺flt3⁺ reconstituting cells. Phenotypic and functional analysis support that Lin⁻Sca1⁺c-kit⁺flt3⁺ cells are progenitors for the common lymphoid progenitor. Thus, upregulation of flt3 expression on Lin⁻Sca1⁺c-kit⁺ HSC cells is accompanied by loss of self-renewal capacity but sustained lymphoid-restricted reconstitution potential.