Oxidative damage produced by oxygen free radicals has been investigated in various mammalian cells in culture. Incubation of these cells with redox cycling quinones resulted in a stimulation of superoxide anion and hydrogen peroxide formation. Further metabolism of H2O2 by glutathione peroxidase caused oxidation and depletion of cellular glutathione followed by oxidation of protein sulfhydryl groups and cytotoxicity. Several targets susceptible to oxidative modification have been identified, including the mitochondrial, endoplasmic reticular, and plasma membrane Ca2+-translocases. As result, a marked and sustained increase in cytosolic free Ca2+ concentration occurred, followed by the activation of some catabolic Ca2+-dependent processes, namely phospholipases, proteases, and endonucleases. In addition, an impairment of the transmembranal signal-transducing system(s) was found. Recent investigations demonstrated that several modifications occur also in the cytoskeleton of oxidative stress-challenged cells. They mainly consist of oxidative actin cross-linking and dissociation of the cytoskeleton from the plasma membrane. All these alterations appear to contribute to the multifactorial process underlying the irreversible cell injury caused by oxidative stress.