Middle-aged workingmen (N=984) with no present medical treatment were enrolled to determine whether there is an association between the metabolic syndrome (MetS) and serum levels of C-reactive protein. MetS was defined as follows: waist circumference > or = 85 cm as a necessary criterion; in addition, two or more of the following criteria were required: serum triglycerides > or = 150 mg/dL and/or highdensity lipoprotein cholesterol <40 mg/dL; systolic blood pressure > or = 130 mm Hg and/or diastolic blood pressure > or = 85 mm Hg; fasting blood glucose > or = 110 mg/dL. Three groups were identified by the components of MetS: a reference group of subjects with a waist circumference <85 cm; group A, with a waist circumference > or = 85 cm with no or one additional MetS criterion; and group B, subjects satisfying the criteria for a diagnosis of MetS. Logistic regression analysis revealed that the components of MetS contributed significantly to serum levels of C-reactive protein. The odds ratios were 2.5 (group A) and 4.0 (group B), when 3 mg/L was adopted as the cutoff value of C-reactive protein.