Abstract-Vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1) are essential for vascular development, but this dependency has been assumed not to persist into adult life. In this study, we report that after 10 days of systemic treatment of 4-, 8-, and 16-week-old mice with VEGF-Trap, an inhibitor of VEGF, the number of capillaries in the tracheal mucosa was reduced by 39%, 28%, and 14%, respectively. The magnitude of the reduction decreased with age (r 2 ϭ0.6, PϽ0.001), but was still significant at 16 weeks. A corresponding age-related decrease in vascular endothelial growth factor receptor-2