Uremic syndrome is associated with several metabolic disturbances. Oxidative stress is an important factor involved in the pathologic mechanism of these changes. The goal of this study was to understand the relationship between oxidative stress markers and two compounds included among uremic toxins. Two independent studies were performed, one with 29 peritoneal dialysis patients and the other with 43 predialysis subjects. In both groups of patients, known oxidative stress markers, malonyldialdehyde (MDA) and carbonyl groups (CG) formation were measured. Additionally, in the predialysis group, glutathione in erythrocytes (GSH) was estimated. In peritoneal dialysis patients, the concentration of advanced glycation end products (AGEs) was found to be significantly increased and correlated with both markers of oxidative stress. In predialysis patients, the increment of newly described uremic toxin purine nucleotide end products (Me2PY and Me4PY) were found and significant correlation was observed between both compounds versus MDA (positive) and GSH (negative). This relationship was visible especially in patients with more advanced renal failure. CG concentration was within the normal values and did not show any correlation with estimated toxin concentrations. In summary, results of both studies suggest that the interrelationship between uremic toxicity and oxidative stress is an important component of uremic syndrome. Nevertheless, further complex studies are needed to elucidate closer pathogenic links.