Ex vivo gene transfer is emerging as a promising therapeutic approach to human neurodegenerative diseases. By combining efficient methodologies for cell amplification and gene delivery, large numbers of cells can be generated with the capacity to synthesize therapeutic molecules. These cells can then be transplanted into the degenerating central nervous system (CNS). Applying this approach to human diseases will require the development of suitable cellular vehicles, as well as safe gene delivery systems capable of tightly controlled transgene expression. For such brain repair technologies, human neural progenitors may be extremely valuable, because of their human CNS origin and developmental potential. We have used these cells to develop a system for the regulated expression of a gene of therapeutic potential. We report the construction of a single adenovirus encoding human tyrosine hydroxylase 1 (hTH-1) under the negative control of the tetracycline-based gene regulatory system. Human neural progenitors infected with this vector produced large amounts of hTH-1. Most importantly, doxycycline allowed a reversible switch of transgene transcription both in vitro and in vivo. This system may be applied to the development of therapies for human neurodegenerative diseases.