Experiments were performed on the chorio‐allantoic membrane (CAM) of the chick to evaluate the effects of bombesin (BN) on vascular neoformation. In morphometrical assays, 10⁻¹³–10⁻⁴ M BN promoted dose‐dependent vascular development. Newly formed vessels converged toward the BN release site in a spoked wheel arrangement, suggesting a diffusion gradient mechanism. Structural and ultrastructural analysis of CAM specimens collected near the BN release site showed that both vasculogenetic and angiogenetic processes cooperated in vascular neoformation that involved committed cells from the mesenchyme (angioblasts) as well as endothelial cells. No pattern of vascular development was detected away from the BN release site. Findings from the present study emphasize the role of BN in vascular net development of respiratory organs. J. Morphol., 2008. © 2007 Wiley‐Liss, Inc.