Although evidence suggests the link between chronic inflammation and oxidative stress as the main mechanism responsible for endothelial dysfunction and cardiovascular complications in patients with metabolic syndrome, little is known about the determining role of each metabolic syndrome component in such alterations. This study investigated the relation between systemic oxidative alterations and metabolic syndrome features in 41 patients. Compared with control subjects, serum vitamin C and alpha-tocopherol concentrations were lower and those of lipid peroxides [thiobarbituric acid reactive substances (TBARs)] were higher in metabolic syndrome patients (P < 0.001). A linear relation was observed between visceral fat thickness and serum TBARs:cholesterol ratio (r = 0.541, P < 0.001), whereas negative correlations were found between alpha-tocopherol and BMI (r = -0.212, P < 0.05) and the grade of liver steatosis (r = -0.263, P < 0.02). Patients with metabolic syndrome and liver steatosis had higher serum hyaluronate (HA) concentrations (P < 0.001). Serum HA was positively correlated with serum alanine amino transferase (r = 0.715, P < 0.001) and the homeostasis monitoring assessment index (r = 0.248, P < 0.03). The presence of metabolic syndrome was predicted from a linear combination of visceral fat and all oxidative variables. In metabolic syndrome patients, serum nitrosothiols and vitamin C concentrations, which were lower (P < 0.001) than in control subjects, were inversely related to the grade of hypertension (r = -0.645, P < 0.001 and r = -0.415, P < 0.007, respectively). In conclusion, metabolic syndrome patients exhibited decreased antioxidant protection and increased lipid peroxidation. Our results indicate a strong association between increased abdominal fat storage, liver steatosis, and systemic oxidative alterations in metabolic syndrome patients and diminished nitrosothiols and vitamin C concentrations as important factors associated with hypertension in these patients.