Lipid peroxidation (LPO) was evaluated in 31 patients with nephrolithiasis and chronic pyelonephritis in remission. Chronic inflammation of renal parenchyma is shown to be associated with LPO activation. Urine diene conjugates excretion, plasma and red cell membrane malonic dialdehyde concentrations increase. LPO activation may contribute to maintenance of chronic renal inflammation in nephrolithiasis.