Individuals with sickle-cell disease (SCD) and transgenic sickle mice expressing human βS globin exhibit enhanced reactive oxygen species (ROS) production, vascular inflammation, and episodic vasoocclusion. We hypothesize that reduction of ROS will reduce endothelial-cell activation and adhesion-molecule expression, thereby inhibiting vasoocclusion. To test this hypothesis, we measured endothelial-cell activation, adhesion-molecule expression, and vasoocclusion in sickle mice after administering IV polynitroxyl albumin (PNA), a superoxide dismutase and catalase mimetic. Untreated sickle mice, compared with normal mice, showed increased activation of nuclear factor-κB (NF-κB), an oxidant-sensitive transcription factor, in their lungs, livers, and skin. NF-κB activation was increased further in the livers and skin of sickle but not normal mice after hypoxia-reoxygenation. IV administration of PNA inhibited NF-κB activation by 60% (P <. 01) in the lungs and by 33% (P <. 05) in the livers of sickle mice after hypoxia-reoxygenation. PNA also reduced the expression of vascular cell-adhesion molecule-1 (VCAM-1) by 57% in lung (P <. 05) and by 33% in liver (P <. 05) and reduced the expression of intercellular-adhesion molecule-1 (ICAM-1) by 40% in lung (P <. 05) and by 53% in liver (P <. 05). PNA inhibited a hypoxia-reoxygenation-induced increase in leukocyte rolling (P <. 01) and adhesion (P <. 05) in venules of the dorsal skin. Most importantly, PNA completely inhibited hypoxia-reoxygenation-induced vasoocclusion (P <. 001). Control albumin had no effect on NF-κB, VCAM-1, ICAM-1, rolling, adhesion, or vasoocclusion. We speculate that therapies to reduce oxidative stress will inhibit inflammation and vasoocclusion in SCD.