Baseline deta for the 12 866 men from the Multiple Risk Factor Intervention Trial was used to study factors related to white blood cell (WBC) count. White blood cell count was significantly higher in smokers (7853 cells/mm3) and exsmokers (7091 cells/mm3) who stopped smoking less than one year before than in ex-smokers who stopped more than one year before (6255 cells/mm3) and those who never smoked (6094 cells/mm3). In current cigarette smokers, white blood cell count was significantly related to number of cigarettes smoked, degree of inhalation, and duration of smoking (p<0.001 for each). In addition, white blood cell count was higher in non-cigarette smokers who smoked pipes, cigars, or cigarillos than among men who did not smoke tobacco (p<0.001). White blood cell count was lower in blacks (by 877 cells/mm3) and Orientals (by 634 cells/mm3) than in whites. Leukocyte count also showed a strong inverse association with high density lipoprotein (HDL)-cholesterol, a positive association with triglycerides independent of cigarette use, and a positive association with low density lipoprotein (LDL)-cholesterol in smokers only. Leukocyte counts were inversely related to total family income and alcohol consumption. We conclude that elevated leukocyte count is independently associated with other risk factors for coronary heart disease (CHD) such as amount and duration of smoking as well as an atherogenic profile, and these relationships should be considered when using white blood cell count as a predictor of coronary heart disease.