Lipid peroxidation is initiated by the production of oxygen-free radicals; it is increased in a wide variety of diseases, including various hemolytic anemias, and in hemoglobin disorders. Increased lipid peroxidation occurs in red cells in the presence of reactive iron species and some heme moieties. In this study, greatly reduced concentrations of malondialdehyde, an indicator of lipid peroxidation, were observed in stored blood upon the addition of both deferoxamine mesylate and diethylenetriaminepentaacetic acid (p less than 0.001). The antioxidant glutathione was much less effective (p less than 0.01 or less than 0.05, depending on incubation time). On the other hand, the addition of dimercaptosuccinic acid and ascorbic acid both significantly increased malondialdehyde production over controls (p less than 0.001 and p less than 0.05, respectively). Ascorbic acid, in the presence of deferoxamine mesylate, added no red cell protection over that of deferoxamine mesylate alone. The addition of metal chelators and, possibly, certain antioxidants to stored blood may be effective in increasing the viability and longevity of transfused red cells.