Human neural precursor cells.(hNPCs), harvested from somatic tissue and grown in vitro, may serve as a Source of cells for cell replacement strategies aimed at treating neurodegenerative disorders such as Parkinson's disease (PD), Huntington's disease (HD), and intractable spinal cord pain. A crucial element in a robust clinical production method for hNPCs is a serum-free growth medium that can support the rapid expansion of cells while retaining their multipotency. Here, we report the development of a cell growth medium (PPRF-h2), for the expansion of hNPCs, achieving an overall cell-fold expansion of 10(13) over a period of 140 days in stationary culture which is significantly greater than other literature results. More importantly, hNPC expansion could be scaled-up from stationary culture to suspension bioreactors using this medium. Serial subculturing of the cells in suspension bioreactors resulted in an overall cell-fold expansion of 7.8 x 10(13) after 140 days. These expanded cells maintained their multipotency including the capacity to generate large numbers of neurons (about 60%). In view of our previous studies regarding successful transplantation of the bioreactor-expanded hNPCs in animal models of neurological disordes, these results have demonstrated that PPRF-h2 (confactor and human leukemia inhibitory factor) can successfully facilitate the production of large quantities of hNPCs with potential to be used in the treatment of neurodegenerative disorders. Biotechnol. Bioeng. 2010;105: 823-833. (C) 2009 Wiley Periodicals, Inc.