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Objectives: Previous studies have investigated the role of oxidative stress in the etiology of generalized anxiety disorder (GAD). Thiols are an important component of the antioxidant buffer system. Dynamic thiol/disulphide homeostasis is a system that has a significant role in processes such as antioxidation preservation and regulation of enzymatic reactions. However, the value of dynamic thiol/disulphide homeostasis in etiopathogenesis of GAD has not been documented. The goal of this study was to determine dynamic thiol/disulphide homeostasis, which has an important role in antioxidant defense in untreated patients with GAD. Methods: This study included 25 patients who were diagnosed with GAD and 24 age-matched healthy controls. In both groups, thiol/disulphide homeostasis was assessed using an automated assay method. The Hamilton Anxiety Rating Scale (HAM-A) was used to determine the anxiety levels of patients with GAD.Results: Patients with GAD had higher total thiol and native thiol levels compared to the control group, but the differences were not statistically significant. In patients with GAD, the dynamic disulphide levels, disulphide/native thiol, and disulphide/total thiol ratios were higher compared to the control group. However, the native thiol-to-total thiol ratio was significantly lower in patients with GAD compared to the control group (p=0.020). Pearsons correlation analysis showed no statistically significant correlations between total HAM-A scores and oxidative stress parameter levels in the patient group. Conclusions: This is the first report to assess the thiol/disulphide homeostasis in GAD patients. Our study provides evidence that the disulphide-to-native thiol and disulphide-to-total thiol ratios are higher in untreated patients with GAD than in the control group. This suggests that thiol/ disulfide homeostasis is impaired in GAD patients. [Anadolu Psikiyatri Derg 2018; 19(2.000): 143-149]