The work describes the isolation and characterization of CD34+ stem cells from umbilical cord blood using biochemical and biophysical methods. Various non-viral and viral gene transfer methods were employed for the gene transfection of the stem cells. The cytokine effect on transfection efficiency and the stability of reporter gene expression was quantified using different plasmids. The study presents important results from in vivo bioluminescence investigations in immunodeficient NOD/SCID mice. It was found that the non-viral nucleofection method resulted in a high transfection efficiency of CD34 stem cells, but only transient plasmid incorporation was detectable. A moderate efficiency associated with stable gene integration was achieved through retroviral gene transfer. Adenoviral and liposomal reporter gene transfer proved to be less efficient for adult stem cells. In vivo bioluminescence studies demonstrated an accumulation of luciferase-positive cells in the mouse bone marrow during short-term grafting. This work lays the foundation for studies on embryonic stem cells.