Vascular Endothelial Growth Factor-A (VEGF-A) is an endothelial-specific growth factor that induces angiogenesis, i.e., sprouting of capillaries from preexisting vesselsin vivo.Endothelial nitric oxide synthase (eNOS) is an essential molecule in mediating VEGF-A-induced angiogenesis and endothelial function via production of nitric oxide (NO). Moreover, the protein level of eNOS is upregulated in response to VEGF-A. While VEGF-A-induced NO release in human trophoblast cells appears to be initiated via VEGF receptor-1, it is not clear which of the VEGF-receptors is mediating the signal for induction of eNOS protein expression. In addition, it is unclear whether other NOS isoforms are upregulated in response to VEGF-A stimulation. To address these questions, we stimulated human umbilical vein endothelial cells (HUVEC) with VEGF-A for 24 hours and evaluated expression of eNOS and iNOS protein. VEGF-A induces expression of both members of the NOS family. Using porcine aortic endothelial cells overexpressing either VEGF receptor-2 (PAE/KDR cells) or VEGF receptor-1 (PAE/Flt-1 cells), we have studied the regulation of iNOS and eNOS expression in response to VEGF-A stimulation. The activation of VEGF receptor-2 leads to an upregulation of both eNOS and iNOS protein, while stimulation of VEGF receptor-1 did not generate such a signal. Therefore, only VEGF receptor-2 mediates stimulation of eNOS and iNOS expression. We conclude that the two VEGF receptors have different and distinct functions regarding NO formation and NO release during VEGF-A-induced angiogenesis.