The in vitro differentiation potential of mesenchymal stem cells (MSC) into the endothelial lineage was analyzed. MSC were generated out of mononuclear bone marrow cells from healthy donors separated by density gradient centrifugation. Cells were characterized by flow cytometry using a panel of monoclonal antibodies and were tested for their potential to differentiate along different mesenchymal lineages. The differentiation of expanded adult human MSC into cells with phenotypic and functional features of endothelial cells was shown.