Self-renewing and multipotent neural stem cells are present in the adult human brain. We successfully harvested neural stem cells from mice and humans using misexpressed EGFP proteins under the control of the nestin second intron enhancer. High-level EGFP expressors derived from mouse embryos included a distinct subpopulation of cells that were self-renewable and multipotent. Further, we obtained that neural progenitor cells from rat fetal spinal cords using a neurosphere technique, and demonstrated their ability to divide and differentiate into neurons in vivo, where they were integrated into the host tissue in the injured rat spinal cord with resultant behavioral improvement of the recipient rat. We also harvested tyrosine hydroxylase-positive neurons from a transgenic mouse expressing GFP under the control of the tyrosine hydroxylase promoter, and successfully transplanted them into the striatum of rats with parkinsonism with marked improvement of the neurological symptoms. Since neural stem cells can adapt well in the host CNS, studies should focus on their application as a vector in gene therapy and on the introduction in vivo or ex vivo of genes to control their proliferation and differentiation. Neural stem cells are a potential, useful source for developing new therapy for CNS disorders.