Aim: To analyze various oxidative stress parameters in the saliva and serum of patients with chronic renal failure (CRF) and/or diabetes mellitus (DM), and to compare them in dialytic vs. pre-dialytic patients. Method: 50 consenting patients were divided into five subgroups of patients: severe CRF (dialytic) without DM, severe CRF (dialytic) with DM, mild CRF (pre-dialytic) without DM, mild CRF (pre-dialytic) with DM, and with DM but without CRF (controls). Uric acid (UA), peroxidase and total antioxidant status (TAS) were studied in both saliva and serum; superoxide dismutase (SOD) was evaluated only in saliva. Both saliva collection and serum harvesting were done simultaneously. Results: In severe-CRF patients without DM, median TAS, UA and SOD levels decreased following dialysis (54, 85, 48%, respectively), and peroxidase levels increased slightly (9%). In severe-CRF patients with DM, median TAS and SOD levels increased following dialysis (33 and 54%, respectively) while median UA and peroxidase levels decreased (68 and 10%, respectively). Conclusions: DM, CRF and hemodialysis were found to increase the oxidative stress burden in both serum and saliva. Therefore, antioxidant assessment may be used to monitor baseline oxidative status in these situations though larger randomized studies are in order.