Neovascularization by sprouting angiogenesis is critical for inflammation-mediated tissue remodeling and wound healing. We report here that human polymorphonuclear neutrophils (PMN) stimulated for 1 h with 100 nM N-formyl-Met-Leu-Phe (fMLP) released a proangiogenic entity which induced sprouting of capillary-like structures in an in vitro angiogenesis assay. The effect was comparable to the response obtained upon stimulation with 100 ng/ml basic fibroblast growth factor. The PMN-mediated response was inhibited by neutralizing antibodies against VEGF or IL-8. As measured by ELISA technique, we found that fMLPactivated PMN (5 x 10⁶/ml) released 78 pg/ml IL-8 and 39 pg/ml VEGF within 1 h after stimulation. The IL-8 release was blocked by actinomycin D or cycloheximide, but the inhibitors had no effect on the VEGF release suggesting that the IL-8 secretion required de novo synthesis whereas VEGF was secreted from preformed stores. Accordingly, RT-PCR analysis revealed that the IL-8 mRNA was upregulated upon PMN stimulation whereas the expression of the VEGF mRNA was not affected. Moreover, the supernatant derived from activated PMN induced an upregulation of the endothelial IL-8 mRNA expression suggesting that the release of VEGF and IL-8 from activated PMN may activate a paracrine feedforward mechanism involving endothelial IL-8. Moreover, the VEGF-induced upregulation of endothelial IL-8 expression as well as the sprouting of capillary-like structures was inhibited by a neutralizing anti-IL-8 antibody. These findings suggest that bacteria-derived tripeptides stimulate human PMN to release VEGF and IL-8 which activate endothelial cells and induce angiogenesis by a paracrine feedforward mechanism involving endothelial IL-8 upregulation.