In our current gene transfer study being conducted at NIH Clinical Center (Bethesda, MD) and at our institution, use of MRI guidance and relatively high infusion volumes (Richardson et al., 2011) to ensure adequate coverage of the putamen and caudate with AAV2-GDNF should provide a definitive answer to the utility of GDNF in Parkinson's disease in line with encouraging data from stable MPTP-lesioned nonhuman primates (Kells et al., 2010). The gene discussed is GDNF; the disease is Parkinson disease.