There is an increasing body of experimental studies demonstrating the toxic effects of oxygen-derived free radicals. Evidence supports an important role for free radicals in ischemic injuries, inflammation, and chemical-induced tissue injury. Free radicals are involved in normal biochemical processes like oxidative reduction and cellular metabolism; however, they also mediate disease processes. The participation of oxygen free radicals in lysis of red cells is important in some situations of intravascular hemolysis. This article will review neutrophil-derived oxygen free radicals, emphasizing: (1) their effects on the erythrocyte and (2) how these effects may be attenuated.