Rat lung isografts were preserved for 48 hr at 0 degrees C using a simple organ flush technique. After storage alone, isotonic saline flush resulted in significantly raised indices of lipid peroxidation in vitro (Schiff bases and thiobarbituric-acid-reactive material [TBAR]). Lungs flushed with hypertonic citrate (HCA) had significantly less oxidative damage than saline-flushed lungs. The addition to the HCA flush of verapamil, a calcium channel blocker, or desferrioxamine, an iron chelator, significantly reduced TBA reactivity in stored lungs compared with HCA alone. After 1-hr reperfusion in vivo, lipid peroxidation was reduced in HCA-flushed lungs compared with saline flush (TBAR alone), but no additional protection from the use of desferrioxamine or verapamil was demonstrated. Electron microscopy after saline flush and storage alone showed gross endothelial swelling and fragmentation. Reperfusion with blood for 1 hr resolved cell swelling, but alveolar/capillary wall rupture occurred. HCA protected against cell swelling, but endothelial vesiculation and widening of the basement membrane were observed. After reperfusion, HCA-flushed lungs developed much endothelial loss that was considerably reduced by the use of desferrioxamine and verapamil. The lipid peroxidation results suggest that iron- and calcium-mediated free radical production may be important mechanisms in oxidative damage to stored rat lungs. Electron microscopy findings correlated with biochemical evidence of free-radical-mediated injury. Reduction of endothelial loss on reperfusion by the use of verapamil and desferrioxamine provides circumstantial evidence that ischemia and reperfusion damage of organs stored for transplantation is partly due to Fe++(+)- and Ca+(+)-dependent mechanisms that probably involve increased free radical production.