A growing body of evidence suggests that chromogranin A (CgA), a secretory protein released by many neuroendocrine cells and frequently used as a diagnostic and prognostic serum marker for a range of neuroendocrine tumors, is a precursor of several bioactive fragments. This work was undertaken to assess whether the N-terminal fragment CgA_1-76 (called vasostatin I) can inhibit the proangiogenic activity of vascular endothelial growth factor (VEGF), a factor involved in tumor growth. The effect of recombinant human vasostatin I (VS-1) on VEGF-induced human umbilical endothelial cells (HUVEC) signaling, proliferation, migration, and organization has been investigated. We have found that VS-1 (3 µg/ml; 330 nM) can inhibit VEGF-induced ERK phosphorylation, as well as cell migration, proliferation, morphogenesis, and invasion of collagen gels in various in vitro assays. In addition, VS-1 could inhibit the formation of capillary-like structures in Matrigel plugs in a rat model. VS-1 could also inhibit basal ERK phosphorylation and motility of HUVEC, leading to a more quiescent state in the absence of VEGF, without inducing apoptotic or necrotic effects. Conclusion: These findings suggest that vasostatin I may play a novel role as a regulator of endothelial cell function and homeostasis. --Belloni, D., Scabini, S., Foglieni, C., Veschini, L., Giazzon, A., Colombo, B., Fulgenzi, A., Helle, K. B., Ferrero, M. E., Corti, A., Ferrero, E. The vasostatin-I fragment of chromogranin A inhibits VEGF-induced endothelial cell proliferation and migration.