Insulin resistance, an essential core contributing to the metabolic syndrome (MS), has been demonstrated in some studies to be associated with white blood cell (WBC) or red blood cell (RBC) counts. The present study was undertaken to assess systemically the relationship between WBC or RBC counts and various clinical features of MS in a large Chinese population at Taiwan. A total of 4938 subjects (2891 men and 2047 women with a mean age of 50.1 +/- 12.6 years), who had attended health examination at this hospital were enrolled. The Adult Treatment Panel III (ATP III) definition of MS components was adopted in this study with the exception of the definition of obesity. This was defined as body mass index (BMI) greater than 27 kg/m(2). Overall, 14% had high serum total triglyceride (TG), 8% had low high-density lipoprotein (HDL) cholesterol, and 18% were obese. WBC counts showed a statistically significant (P < .001) correlation with TG (r = .265), HDL(r = -.187), fasting glucose (r = .084), and BMI (r = .172) but not with blood pressure levels. In addition, RBC counts correlated significantly (P < .001) with TG (r = .250), HDL(r = -.269), fasting glucose (r = .098), and BMI (r = .228). WBC and RBC counts in subjects grouped according to the presence of 0, 1, 2, and >or= 3 features of MS were 6268 +/- 1633, 6555 +/- 1782, 6995 +/- 1880, and 7185 +/- 1696 cells/mm(3), and 4.63 +/ -0.56 x 10(6), 4.73 +/- 0.54 x 10(6), 4.84 +/- 0.60 x 10(6), and 4.91 +/- 0.55 x 10(6) cells/mm(3), respectively (P for trend <.001). Subjects in the highest quartile of WBC or RBC counts demonstrated a three- or twofold increase, respectively, in the odds ratio for MS with 3 or more metabolic features compared to subjects in the lowest quartile of WBC or RBC counts. Increased WBC and RBC counts, albeit normal, were associated with a variety of MS features in a Taiwan Chinese population, suggesting that hematological parameters could potentially be used as indicators of this syndrome.