It is reported on the results of measurements of the antitoxydative capacity (AC) in the serum of children suffering from chronic renal failure, during hemodialysis and after kidney Transplantation. The results show in comparison with healthy children (19.95 +/- 5.22 mm, n = 19) that children suffering from chronic renal failure may develop an increased AC (66.18 +/- 29.14 mm, n = 24). In dialyzed children different values are found previous and after hemodialysis (58.11 +/- 9.25 vs. 17 +/- 3.6 mm). Children show after transplantation the highest values (78.9 +/- 26.04 mm, n = 13). If the increase of the AC is a compensatory and regulatory mechanism or the result of accumulation of antioxydative substances should realized in further investigations. The measurements of vitamin-E-supplemented sera may show that an oral application of vitamin E increase the AC in vivo.