The possibility that controllable environmental factors such as passive smoking and non-breast feeding contribute substantially to wheezing has implications for prevention. Effects of passive smoking and non-breast feeding on wheezing in children aged 6 to 10 years were explored in a historical cohort study of 223 children. Family history of respiratory allergy or asthma, male sex, maternal smoking, and non-breast feeding were significantly associated (p less than 0.05) with wheezing in bivariate analysis. In multivariate loglinear analyses, predictors of wheezing included non-breast feeding (p = 0.05, odds ration = 2.1), male sex (p less than 0.03, odds ratio = 3.1), and family history of respiratory allergy (p less than 0.03, odds ratio = 2.6). In a second model, predictors included an interaction of maternal smoking and family history (p less than 0.005, odds ratio = 4.6) in addition to male sex and family history of respiratory allergy. In further exploration based on tabular analysis, maternal smoking appeared to increase wheezing among children in whom the family history of respiratory allergy was positive (p less than 0.001). Among children in whom the family history of respiratory allergy was negative, non-breast feeding appeared to increase wheezing (p = 0.01). Promotion of breast feeding and reduction of maternal smoking might reduce childhood wheezing.