Abstract: Disclosed is a method for alleviating the oxidative impairment of vascular function by inhibiting the activity of xanthine oxidase, or active forms thereof. Xanthine oxidase levels have been shown to be increased by a variety of conditions, including sickle cell disease. In the present disclosure, allopurinol is used to inhibit xanthine oxidase activity. As a result of the inhibition of xanthine oxidase, .NO levels in a subject can be maintained. In addition to sickle cell disease, allopurinol inhibition of xanthine oxidase may be used to treat other conditions, including, but not limited to, respiratory distress, kidney disease, liver disease, ischemia-reperfusion injury, organ transplant, sepsis, burns, viral infections and hemorrhagic shock.