Multipotent human mesenchymal stem cells can be isolated from bone marrow and expanded more than 1-billion-fold in cell culture without the loss of their stem cell capacity. In addition, human mesenchymal stem cells can be transduced with genes for reporter molecules or secreted, circulating cytokines; these genes can be inserted into the genomes of mesenchymal stem cells without affecting their stem cell capacity. Thus, the stage is set for the use of mesenchymal stem cells as curative agents in genetic disorders involving skeletal tissues.