Background: Increased intrahepatic vascular tone in cirrhosis has been attributed to a decrease of hepatic nitric oxide (NO) secondary to disturbances in the post-translational regulation of the enzyme eNOS. NO scavenging by superoxide (O2−) further contributes to a reduction of NO bioavailability in cirrhotic livers. Aim: To investigate whether removing increased O2− levels could be a new therapeutic strategy to increase intrahepatic NO, improve endothelial dysfunction and reduce portal pressure in cirrhotic rats with portal hypertension. Methods: Adenoviral vectors expressing extracellular superoxide dismutase (SOD) (AdECSOD) or β-galactosidase (Adβgal) were injected intravenously in control and CCl4-induced cirrhotic rats. After 3 days, liver O2− levels were determined by dihydroethidium staining, NO bioavailability by hepatic cGMP levels, nitrotyrosinated proteins by immunohistochemistry and western blot, and endothelial function by responses to acetylcholine in perfused rat livers. Mean arterial pressure (MAP) and portal pressure were evaluated in vivo. Results: Transfection of cirrhotic livers with AdECSOD produced a significant reduction in O2− levels, a significant increase in hepatic cGMP, and a decrease in liver nitrotyrosinated proteins which were associated with a significant improvement in the endothelium-dependent vasodilatation to acetylcholine. In addition, in cirrhotic livers AdECSOD transfection produced a significant reduction in portal pressure (17.3 (SD 2) mm Hg vs 15 (SD 1.6) mm Hg; p<0.05) without significant changes in MAP. In control rats, AdECSOD transfection prevents the increase in portal perfusion pressure promoted by an ROS-generating system. Conclusions: In cirrhotic rats, reduction of O2− by AdECSOD increases NO bioavailability, improves intrahepatic endothelial function and reduces portal pressure. These findings suggest that scavenging of O2− might be a new therapeutic strategy in the management of portal hypertension.