Hemodialysis (HD) patients are exposed to high oxidative stress, however, the nature of this stress is still unclear. In this study, we employed a specific lipid peroxidative product, phosphatidylcholine hydroperoxide (PCOOH), and evaluated the peroxidative effect of end stage renal disease by measuring thiobarbituric acid reactive substances (TBARS) and PCOOH in both plasma and erythrocyte membrane. We also surveyed plasma TBARS and PCOOH before and after HD sessions thereby assessing oxidative stress by a single HD procedure. The plasma TBARS level of healthy controls was 2.9 ± 0.4 nmol/ml. Those of HD patients before and after HD session were 5.1 ± 1.4 and 3.1 ± 0.5 nmol/ml, respectively, and the pre-HD plasma TBARS levels were significantly higher than those of controls and after HD. The Plasma PCOOH concentration of patients before HD was 119.7 ± 58.4 pmol/ml and was significantly higher than that of controls which was 88.6 ± 14.3 pmol/ml. After HD, the plasma PCOOH level decreased to 103.2 ± 36.0 pmol/ml, which was still significantly higher than that of controls. In erythrocytes, the PCOOH level of patients was 259.3 ± 105.4 nmol/g RBC and was significantly higher than that of controls with 88.6 ± 32.0 nmol/g RBC. Analyzed with respect to the cause of renal disease, the polycystic kidney disease patients showed significantly lower plasma PCOOH levels than the others. These results suggest that there is an increase of lipid peroxidation in both plasma and erythrocytes of HD patients, though this oxidative stress was not brought about by HD.