We recently reported that intermittent hypoxia facilitated the proliferation of neural stem⁄progenitor cells (NPCs) in the subventricule zone and hip-pocampusin vivo. Here, we demonstrate that hypoxia promoted the prolif-eration of NPCsin vitro and that hypoxia-inducible factor (HIF)-1a, which is one of the key molecules in the response to hypoxia, was critical in this process.