This study focuses on the oxidative stress in patients with severe chronic renal failure who are not undergoing dialysis treatment. The erythocyte levels, creatinine clearing and plasma- and cell activities of the following enzymes were determined: glutathione peroxidase (Gpx), superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione transferase (GT). The concentrations of non-enzyme molecules such as total glutathione in both oxidized and reduced forms, and malonyldialdehyde (MDA) were also measured. The obtained values were compared with those in healthy blood donors of comparable age and social status. The results indicate that chronic renal patients have lower glutathione levels and reduced activities of glutathione peroxidase and of glutathione reductase, while exhibiting elevated levels of malonyldialdehyde and activities of superoxide dismutase, glutathione transferase, and catalase. Finally, creatinine clearing was found to be correlated (p < 0.001) to total (oxidized and reduced) glutathione, Gpx and MDA. These observations may serve to establish a simple protocol for evaluation of renal function.