In recent years, increasing clinical and experimental data have provided compelling evidence that neutrophil-derived oxygen radicals and their metabolites are important mediators of vascular endothelial injury. In this review, attention is directed toward in vitro, ex vivo, and in vivo experimental studies contributing to current understanding of mechanisms of oxyradical mediated endothelial damage. Although these studies may have broad significance, they appear to have particular relevance to the pathogenesis of the adult respiratory distress syndrome and other types of acute pulmonary dysfunction.