There are conflicting reports on the effects of atopy on lung function. The purpose of this study was to compare the effects of house mite (HM) atopy on lung function in subsamples of 12-year-old symptomatic and nonsymptomatic preadolescent children taken from the community sample. An additional objective of this study was to identify possible environmental determinants of HM skin reaction. We obtained questionnaire data on respiratory symptoms and skin-prick tests and performed spirometry on a subsample of 311 children of a birth cohort of children who have been followed over 3 years. Multivariate regression analysis showed progressive decrement of lung function indices (forced vital capacity, forced expiratory volume in 1 sec, and forced expiratory flow, midexpiratory phase) with increasing degree of HM atopy reflected by the skin reaction to HM allergens. The apparent association between the level of HM atopy and the lung function indices was highly significant in symptomatic individuals but insignificant in nonsymptomatic subjects. HM sensitization was significantly associated with mother's atopy. It occurred predominantly in boys and was related to the use of coal or gas for house heating. The effect of allergen sensitization on lung size and airway caliber confined to symptomatic subjects may reflect the inflammatory status of bronchial airways in the symptomatic subjects.