A total of 1,035 swabs from 345 healthy pre-school children - 268 attending day care centers (DCC group) and 77 staying at home were taken. The statistically significant difference in Haemophilus influenzae colonization was observed among children exposed and unexposed to tobacco smoke in the total population (p=0.042) and in the DCC group (p=0.034). H. influenzae prevalence among passive smoking children prone to recurrent respiratory infections was higher compared to unexposed children in the total population (p=0.084) or in DCC group (p=0.032). This suggests that passive smoking and attending DCC may predispose H. influenzae colonization of the upper respiratory tract in pre-school children.