The aims of the present study were to assess the effects of maternal use of domestic chemicals during pregnancy on wheezing and lung function in children aged </=8.5 yrs and to explore the potential modifying effect of atopy. In the Avon Longitudinal Study of Parents and Children, a cohort study, a maternal composite household chemical exposure (CHCE) score was derived. Wheezing phenotypes from birth to age 7 yrs were assigned on the basis of reported wheeze. Lung function (forced expiratory volume in one second (FEV(1)), forced vital capacity (FVC), forced midexpiratory flow between 25 and 75% of FVC (FEF(25-75%))) was measured at age 8.5 yrs; and atopy by skin-prick tests at age 7.5 yrs. Multinomial logistic and linear regression models assessed the relationship between wheezing outcomes, lung function and CHCE score, and interactions with atopy. Increased CHCE score was associated with early- (<18 months) and intermediate- (18-30 months) persistent and late-onset (>30 months) wheezing in nonatopic children (adjusted odds ratio per z-score of CHCE (95% confidence interval) 1.41 (1.13-1.76), 1.43 (1.02-2.13) and 1.69 (1.19-2.41), respectively). Increasing CHCE score was associated with decrements in FEV(1) and FEF(25-75%). Higher domestic chemical exposure during pregnancy was associated with persistent wheeze and lung function abnormalities in nonatopic children. This may result from pre-natal developmental effects or post-natal irritant effects on the developing airway, but is unlikely to be mediated through increased hygiene in the home.