The beneficial effects of mesenchymal stem cells (MSCs) are mediated partly by the paracrine production of cytoprotective and trophic factors. Vascular endothelial growth factor (VEGF) is released from MSCs as a paracrine trophic factor and contributes to the therapeutic effects of the stem cell by regulating angiogenesis and promoting revascularization in injured tissues. Interleukin-8 (IL-8), an inflammatory chemokine with potent proangiogenic properties, is upregulated in the ischemic brain and has been shown to promote homing of bone marrow-derived cells to injured sites. However, the effect of IL-8 on MSCs paracrine function remains unknown. We found that IL-8 induced VEGF production and phosphorylation of Akt and ERK. Both effects could be blocked by inhibitors (LY294002, PD098059) or siRNA-mediated silencing of Akt and ERK in human bone marrow MSCs (hBM-MSCs). IL-8-induced VEGF production in hBM-MSCs significantly increased tube formation on Matrigel compared with basal secreted VEGF. In a rat stroke model, administration of IL-8-treated hBM-MSCs decreased the infarction volume and increased angiogenesis in the ischemic boundary zone compared with hBM-MSC treatment alone. In conclusion, IL-8 stimulates VEGF production in hBM-MSCs in part via the PI3K/Akt and MAPK/ERK signal transduction pathways and that administration of IL-8-treated hBM-MSCs increases angiogenesis after stroke. This approach may be used to optimize MSC-based therapies for numerous diseases including stroke, myocardial ischemia, and spinal cord injury.