['The role of different risk factors for bronchial hyperresponsiveness (BHR), such as gender, atopy, IgE, and environmental factors (smoking, occupational exposure, infections), has been described. Indoor and outdoor pollution play an important role too, but few studies have analyzed the association with BHR. The aim of this study was to assess the effect of urban residence on BHR.', 'We studied two general population samples enrolled in two cross-sectional epidemiological studies performed in Northern Italy (Po Delta, rural area) and Central Italy (Pisa, urban area). We analyzed 2,760 subjects (age range, 8 to 74 years). We performed analysis of variance and logistic regression analysis using ln slope of the dose-response curve of the methacholine challenge test as dependent variable, and sex, age, smoking habits, respiratory symptoms, skin-prick test results, IgE value, residence, and airway caliber as independent variables.', 'The mean value of ln slope of the dose-response curve adjusted for initial airways caliber (by baseline FEV(1) percentage of predicted value) was significantly higher in female subjects, in smokers, in subjects with respiratory symptoms, in younger and older ages, in subjects with high values of IgE, and in subjects with positive skin-prick test results. After controlling for the independent effects of all these variables, living in urban area was an independent risk factor for having BHR (odds ratio, 1.41; 95% confidence interval, 1.13 to 1.76).'] Is urban residence associated with bronchial hyperresponsiveness in Italian general population samples?