AIM and METHODS: To study the culture met ho d of human neural stem/progenitor cells, these cells derived from human fetal fo rebrains were maintained and expanded in serum-free defined medium containing ba sic fibroblast growth factors (bFGF), epidermal growth factor (EGF) and B27. Whe n they formed neurosphere, these three factors and supplemented FBS were removed to induce differentiation. Cell were cultured for 12-14 d, then fixed for immun ocytochemistry examination. RESULTS: This period of expansion resulted in a 107-fold incre ase in this heterogeneous population of cells. Upon differentiation, they form n eurons, astrocytes and oligodendrocytes, the three main phenotypes in the CNS. CONCLUSION: These results demonstrate the feasibility of long-t erm in vitro expansion of human neural progenitor cells. The advantages of s uch a population of neural precursors for allogeneic transplantation, including t he ability to provide an expandable, well-characterized, defined cell source, ca n form specific neuronal or glial subtypes.