Stem cell transplantation to replace damaged tissue or correct metabolic disease holds the promise of helping a myriad of human afflictions. Although a great deal of attention has focused on pluripotent stem cells derived from embryos, adult stem cells have been described in a variety of tissues, and they likely will prove to be as beneficial as embryonic stem cells in cell replacement therapy and control of inbred errors of metabolism. We describe methods by which stem cells can be introduced into the nervous system, although the techniques are applicable to any portion of the body to be targeted or any cell that may be used for cell therapy. The first and most straight-forward method is introduction of stem cells directly into the brain parenchyma. The second, which in our hands has proven to be superior in some instances, is introduction of the stem cells into the circulatory system.