AIMS: Increased endothelin-1 (ET-1) is a hallmark of pulmonary arterial hypertension (PAH), and contributes to its pathogenesis. The factors controlling ET-1 in PAH are poorly understood. Combined with other stimuli, vascular endothelial growth factor (VEGF) blockade results in PAH-like lesions in animal models, and has been associated with PAH in humans. The effects of VEGF on ET-1 production by human lung blood microvascular endothelial cells (HMVEC-LBl) are unknown. MAIN METHODS: We exposed HMVEC-LBl in-vitro to human VEGF-121 (40ng/mL) in serum-free medium for 7h, in the absence or presence of the VEGF receptor antagonist, SU5416 (3 and 10µM). ET-1 production was measured in the supernatant. Phosphorylation of VEGF receptor 2 (VEGFR2) was measured by Western blotting after exposure to VEGF without or with SU5416 for 5 and 10min. KEY FINDINGS: VEGF effectively caused VEGFR2 phosphorylation, which was blocked by SU5416. VEGF decreased ET-1 production by at least 29%. In the absence of VEGF, SU5416 increased ET-1 production, by 16% at 10µM, and SU5416 was able to completely abolish the VEGF effect on ET-1 production. SIGNIFICANCE: VEGF may promote vascular health by decreasing ET-1 production in HVMEC-LBl. Blockade of VEGF signaling by SU5416 increases ET-1 levels. The role of VEGF in modulating endothelin production in PAH deserves further study.