Backround: Oxidative stress (OS) has been implicated in pathogenesis of human disorders such as depressive disorder, sepsis, cardiovascular disease, acute and chronic pancreatitis, and cancer. Increased OS is result of imbalance between increased reactive oxygen and nitrogen species (RONS) production and / or insufficient activity of antioxidant defence system. Antioxidant system, which is composed of antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidases (GPX), glutathione reductase (GR) and non- enzymatic antioxidant reduced glutathione (GSH) plays an important role in the protection of cells against enhanced OS. The aim of this study was to assess the OS markers and antioxidant enzymes in different pathophysiological states. Materials and methods: Activities of erythrocyte glutathione peroxidase (GPX1), GR and concentration of GSH as well as levels of OS markers were analysed in six different pathophysiologic states. These parameters were measured in 35 women with depressive disorder (DD), 40 patients with metabolic syndrome (MetS), 30 septic patients (S) followed up in the course of sepsis; 15 non-septic critically ill patients (NC), 13 patients with acute pancreatitis (AP), 50 with chronic pancreatitis (CP) and 50 patients with pancreatic cancer (PC), compared to..