Reactive oxygen intermediates such as hydrogen peroxide play an important role in the pathophysiology of acute lung injury, not only as terminal effectors, but also as second messengers in signal transduction; we studied their role in adhesion molecule expression and cytokine production. N-acetylcysteine, an antioxidant, decreased the TNF alpha-induced expression of intercellular adhesion molecule-1 on cultured epithelial cells from human bronchi (BEAS-2A), and inhibited IL-8 production by those cells. In vivo, N-acetylcysteine attenuated the sequestration of polymorphonuclear neutrophils in rat lungs caused by intratracheal lipopolysaccharide. These findings suggest that adhesion molecule expression and cytokine production in the lung are mediated by the production of reactive oxygen intermediates. Because adhesion molecules and cytokines play a crucial role in the pathophysiology of neutrophil-mediated acute lung injury, the inhibition of adhesion molecule expression and cytokine production with anti-oxidants such as N-acetylcysteine may be a useful therapeutic strategy.