While airway hyperresponsiveness is usually associated with a diagnosis of asthma or symptoms of wheezing, some individuals with rhinitis show airway hyperresponsiveness as do some with no symptoms whatsoever. We have studied the correlations between symptoms, airway hyperresponsiveness and atopy as determined by skin-prick tests in a cohort of New Zealand children. A total of 662 members of a birth cohort were studied at age 13 years using a respiratory questionnaire, skin-prick tests to 11 common allergens, and an abbreviated validated methacholine challenge test to determine airway responsiveness. Airway hyperresponsiveness (methacholine PC20 FEV1 < or = 8 mg/ml) was strongly correlated with reported asthma and current wheezing (P<0.0001) and also with atopy, especially to house dust mite and cat (P<0.0001). As weal size for both house dust mite and cat increased, so did the proportion of children with airway hyperresponsiveness. All children with diagnosed asthma and airway hyperresponsiveness were atopic. Skin-test reactions to house dust mite and cat were strongly correlated with any degree of measurable airway responsiveness (PC20 FEV1 < or = 25 mg/ml) in children with rhinitis (P<0.00001), and remained significantly correlated even in children without current asthma, without asthma ever and without rhinitis (P<0.001). Atopy is a major determinant of airway hyperresponsiveness in children, not only in those with reported histories of asthma and wheezing, but also in the absence of any history suggesting asthma and rhinitis.