We assessed the association of white blood cell (WBC) count with different components of metabolic syndrome (MS)-obesity, hypertension, hypercholesterolemia, low high-density lipoprotein cholesterol levels, hypertriglyceridemia, high fasting plasma glucose levels and hyperuricemia-in 5275 Japanese male office workers aged 23-59 years. After controlling for age, smoking and alcohol intake, the relative risks for the presence of 1, 2, 3, 4 and greater than or equal to5 features of MS compared with the lowest quintile of WBC count increased in a dose-dependent manner as WBC count increased (P for trend < 0.001 for all) and the increased relative risks for clustered features of MS were more pronounced as the number of features of MS increased. The WBC count increments in subjects with 1, 2, 3, 4 and greater than or equal to5 features of MS were 0.28, 0.45, 0.68, 0.76 and 1.40 x10(9) cells/l, respectively, compared with the subjects without features of MS (P for trend < 0.001). These findings indicate a strong association between WBC count and clustered features of MS in middle-aged Japanese men.