Recent studies have convincingly demonstrated that adult bone marrow contains cells capable of differentiating into a variety of cell types. To investigate whether such bone marrow-derived cells participate on self-renewal and proliferation of nonhematopoietic tissues, we studied tissue obtained by autopsy from female recipients after sex-mismatched allogeneic bone marrow and stem cell transplantation for the presence of donor-derived cells. Epithelial, endothelial, and smooth muscle cells and hematopoietic cells were characterized by double-staining immunohistochemistry with a panel of antibodies and nonisotopic in situ hybridization with a Y-chromosome-specific probe. The present study showed that the capillary endothelium was the only nonhematopoietic cell type that was replaced in a significant amount by donor cells after allogeneic stem cell and bone marrow transplantation. We could not demonstrate any participation of graft-derived cells on repopulation of cardiomyocytes or epithelial cells of the skin and gastrointestinal mucosa and of hepatocytes.