The malondialdehyde equivalent (MDE) was measured by the thiobarbiturate method quantitatively in serum of healthy children, children suffering from chronic renal failure and after kidney transplantation. In the reference group (n = 19) a serum concentration of 3.98 +/- 0.84 nmol/ml was found. Elevated MDE serum concentrations were measured in all groups suffering from renal disease: groups with various degree of diminished renal function (7.05 +/- 2.12 nmol/ml; n = 24), children treated by chronic hemodialysis (6.38 +/- 0.98 nmol/ml; previous dialysis and 6.27 +/- 0.63 nmol/ml after dialysis, n = 9) and children after renal transplantation (6.59 +/- 1.14 nmol/ml; n = 13). In the hemodialysis group the MDE concentration was not affected by a single dialysis nor by sixth months dialysis course. A cell-damaging lipid peroxidation in children suffering from renal diseases is reflected by the investigations.