An emerging new technology based on genetic engineering of viral vectors that can insert genes into the cells of living organisms may play a significant role in treating disorders of the central nervous system (CNS). Most neurodegenerative disorders affect focal regions of the brain. Preventive and/ or palliative treatment strategies need to be targeted only to the diseased parts of the brain without affecting other regions. Administration of therapeutic genes specifically to the disease-affected regions of the brain may be more beneficial than current treatment strategies, which are largely based on systemically administering small molecules. The latter can result not only in peripheral side effects but also CNS side effects since the drugs can affect both targeted and nontargeted brain sites. In addition, many therapeutic agents are prevented from entering the brain by the blood-brain barrier (BBB). For these reasons, many otherwise potentially useful proteins, such as trophic factors, cannot be administered systemically (1).