In the presence of growth factors (EGF and bFGF), the proliferation capacity of NPCs is higher in mild hypoxia (3–5% O2) than in 20% O2. Severe hypoxia (1–2% O2), however, slows down the proliferation of NPCs. In the absence of growth factors, the differentiation potential of NPCs is affected by different level of oxygen. Mild hypoxia promotes neurogenesis and oligodendrogenesis, whereas severe hypoxia favors the generation of astroglial lineage.