Angiogenic factors exert protective effects on the lung. To investigate the effect of VEGF-B, a factor coexpressed in the lung with VEGF-A, we assessed chronic hypoxic pulmonary hypertension in VEGF-B knockout mice (VEGF-B−/−) and in rats with lung overexpression of VEGF-B induced by adenovirus transfer. No significant difference in pulmonary hemodynamics, right ventricular hypertrophy, distal vessel muscularization, or vascular density was found between VEGF-B−/− and control mice after 3 wk of hypoxia. When overexpressed, VEGF-B₁₆₇ or VEGF-B₁₈₆ had protective effects similar to those of human VEGF-A₁₆₅. Lung endothelial nitric oxide synthase (eNOS) expression was increased by 5 days of hypoxia or VEGF-A adenovirus vector (Ad.VEGF-A) overexpression, whereas VEGF-B₁₆₇ or VEGF-B₁₈₆had no effect. With hypoxia or normoxia, the wet-to-dry lung weight ratio was increased 5 days after Ad.VEGF-A administration compared with control (Ad.nul), Ad.VEGF-B₁₆₇, or Ad.VEGF-B₁₈₆. Endogenous VEGF-B does not counteract the development of hypoxic pulmonary hypertension. However, when overexpressed in the lung, VEGF-B can be as potent as VEGF-A in attenuating pulmonary hypertension, although it has no effect on eNOS expression or vascular permeability.