Vasoactive intestinal peptide (VIP) is a neuropeptide known to regulate proliferation and differentiation in normal and tumoral cells. We previously reported that VIP induced neuritogenesis in human neuroblastoma SH-SY5Y cells cultured in serum-free medium. This neuritogenesis was associated with a regulated expression of neuronal cytoskeleton markers. To further characterize the neuroblastic cell differentiation induced by VIP in human SH-SY5Y cells, we investigated expression of synaptosomal-associated protein of 25 kDa (SNAP-25), a protein implicated in exocytosis associated with different processes, including neurite outgrowth. Western immunoblotting and real-time RT-PCR analyses revealed that VIP increased expression of the SNAP-25 protein and the level of both SNAP-25a and SNAP-25b mRNA isoforms. Immunofluorescence experiments indicated that SNAP-25 was mainly located in neurites and at the plasma membrane in SH-SY5Y cells treated with VIP. RNA interference experiments demonstrated that SNAP-25 was involved in VIP-induced neuritogenesis. In conclusion, SNAP-25 is up-regulated and implicated in neuritogenesis in human neuroblastoma SH-SY5Y cells treated with the neuropeptide VIP.