Metabolic syndrome, i.e. the clustering of visceral obesity, dyslipidemia, hyperglycemia, and hypertension, has become a major public-health challenge worldwide. An acute-phase reactant is one whose level increases by 25% of the standard value during inflammation. Associations of acute-phase reactants with the components of metabolic syndrome among overweight or obese patients has rarely been examined. The CRP, ferritin, fibrinogen, haptoglobin, and ESR levels of 117 consecutive overweight or obese patients were measured. Metabolic syndrome was defined if central obesity was combined with at least two of the following factors: triglyceride level > or = 150 mg/dl or specific treatment for this abnormality, HDL cholesterol < 40 mg/dl in males and < 50 mg/dl in females or specific treatment for this abnormality, systolic/diastolic blood pressures > or = 130/85 mmHg or treatment of previously diagnosed hypertension, and fasting plasma glucose > or = 100 mg/dl or previously diagnosed type 2 diabetes. Eighty-two patients were characterized as having metabolic syndrome and 35 as healthy controls. CRP, haptoglobin, and ESR levels increased with increasing number of components of metabolic syndrome. Ferritin and fibrinogen, in contrast, were increased in patients with metabolic syndrome but did not correlate with the number of components. CRP, haptoglobin, and ESR may add significant information regarding the severity of metabolic syndrome among overweight and obese patients.