Oxygen free radicals and other reactive oxygen species are being postulated as causal agents in an increasing number of pathological conditions. Indeed, some investigators are suggesting that highly destructive reactive oxygen species are the final common path lead- ing to tissue damage following a wide variety of insults including trauma, hypoxia, ischemia, hyperoxia, radiation, some toxins, and even strenuous athletic pursuits. But, as Robert Floyd points out, "Proof of the importance of oxygen free radicals and the oxidative damage they initiate depend on unequivocal evidence for the pres-...