Hemoglobin potently inactivates the nitric oxide (NO) radical via a dioxygenation reaction forming nitrate (NO₃^-). This inactivation produces endothelial dysfunction during hemolytic conditions and may contribute to the vascular complications of hemoglobin-based blood substitutes. Hemoglobin also functions as a nitrite (NO₂^-) reductase converting nitrite into NO as it deoxygenates. We hypothesized that during intravascular hemolysis, nitrite infusions would limit the vasoconstrictive properties of plasma hemoglobin. In a canine model of low and high intensity hypotonic intravascular hemolysis, we characterized the hemodynamic responses to nitrite infusions. Hemolysis increased systemic and pulmonary arterial pressures and systemic vascular resistance. Hemolysis also inhibited NO-dependent pulmonary and systemic vasodilation by the NO-donor sodium nitroprusside. Compared with nitroprusside, nitrite demonstrated unique effects by not only inhibiting hemolysis-associated vasoconstriction, but also by potentiating vasodilation at plasma hemoglobin concentrations <25 microM. We also observed as interaction between plasma hemoglobin level and nitrite to augment nitroprusside-induced vasodilation of the pulmonary and systemic circulation. This nitrite reductase activity of hemoglobin in vivo was recapitulated in vitro using a mitochondrial NO sensor system. Nitrite infusions may promote NO generation from hemoglobin while maintaining oxygen delivery; this effect could be harnessed to treat hemolytic conditions and to detoxify the hemoglobin-based blood substitutes.