It was recently reported that crude bone marrow cells have the ability to differentiate into glomerular mesangial cells. However, the exact nature of the engrafting cells in the bone marrow was not known. We tested the hypothesis that hematopoietic stem cells are capable of reconstituting the mesangial cells by transplanting a clonal population of cells derived from a single stem cell. We cultured Lin⁻, Sca-1⁺, c-kit⁺, CD34⁻ bone marrow cells from transgenic enhanced green fluorescent protein (EGFP) mice (C57BL/6-Ly-5.2 background) individually for 1 week in the presence of interleukin-11 and steel factor. We then transplanted viable clones individually into lethally irradiated C57BL/6-Ly-5.1 mice. Kidneys from 5 recipient mice showing high levels (60%-90%) of multilineage hematopoietic reconstitution were examined 2 to 6 months later, using differential interference contrast and epifluorescence microscopy. EGFP⁺ cells with a morphology characteristic of mesangial cells were evident within the glomeruli. Transplantation of 100 noncultured Lin⁻, Sca-1⁺, c-kit⁺, CD34⁻ bone marrow cells also generated mesangial cells. Cultured EGFP⁺ glomerular cells from recipient mice contracted in response to angiotensin II. EGFP⁺ mesangial cells seen in male-to-male transplants revealed only one Y-chromosome. These data demonstrate that a single hematopoietic stem cell is capable of differentiating into glomerular mesangial cells and that the process does not involve cell fusion.