Dynamic thiol/disulphide homeostasis plays a critical role in numerous intracellular enzymatic pathways including antioxidant defence and detoxification. In this study, we sought to investigate dynamic thiol/disulphide homeostasis in patients with masked hypertension (MHT) and its relationship with blood pressure. Forty patients (23 men, 17 women) with newly diagnosed MHT and not yet on medical therapy, and 40 healthy volunteers (21 men, 19 women) were enrolled. Blood thiol/disulphide homeostasis was measured in both groups. Serum native and total thiol levels were measured using the novel, fully automated colorimetric method developed by Erel et al. Serum disulphide level was calculated as (serum total thiol - serum native thiol)/2. Native and total thiol levels (p = 0.001) and native thiol/total thiol ratio (p = 0.023) were found to be lower in patients with MHT when compared to those of the control group. Disulphide level and ratios of disulphide/native thiol and disulphide/total thiol were higher in patients with MHT than in the control group (p = 0.001). A positive correlation of systolic blood pressure (SBP) and diastolic blood pressure (DBP) was observed with disulphide/native thiol ratio (p < 0.001). Stepwise multivariable regression analysis showed disulphide/native thiol ratio to be an independent risk factor of SBP and DBP, and SBP to be an independent risk factor of disulphide/thiol ratio (p = 0.001). In this study, we found that dynamic thiol/disulphide homeostasis shifted towards disulphide formation due to thiol oxidation in patients with MHT. Prospective randomised controlled studies are required to elucidate whether abnormal thiol/disulphide status lies in the pathogenesis of MHT or is a consequence of MHT.