<i>Background/Aims:</i> Oxidative damage has been reported to be involved in the pathophysiology of chronic kidney disease (CKD) as well as in the pathogenesis of cardiovascular complications of CKD patients. The aim of the present investigation was to evaluate the levels of plasma carbonyl formation, a sensitive marker of enhanced oxidative stress in predialysis, hemodialysis (HD) and peritoneal dialysis (PD) patients. <i>Methods:</i> Plasma samples from 20 apparently healthy control individuals and 127 CKD (stages 2, 3, 4, HD and PD) patients were evaluated by Western blot analysis for the estimation of the levels of protein carbonyl formation. <i>Results:</i> Albumin represented the main plasma carbonylated protein. Increasing carbonylation of albumin was detected along with the severity of CKD, reaching significance at stages 3 and 4 (p < 0.01, compared to healthy controls). The carbonylation of albumin was even higher in the plasma of HD patients (p < 0.001), while in PD patients it was not statistically significant compared to controls (p = 0.224). <i>Conclusions:</i> The data presented in this work indicate that oxidative stress in CKD patients gradually increased during the development of the disease. This stress is probably intensified during HD, but not in PD subjects.