In 105 subjects taken from a student population and aged between 15 and 30 there was a strong positive association between the presence of the atopic state, defined by skin tests, and a high level of non-specific bronchial responsiveness to methacholine (χ2= 10·5, d.f. = 2, P= 0·01). Regression analysis showed a history of asthma, and the symptom of wheeze, to be predominantly predicted by the degree of bronchial responsiveness (R2= 31%), with only a minor independent contribution from the degree of atopy (R2 a furthur 5%). The genetic or other reasons for the association between bronchial responsiveness and atopy may have importance in understanding the aetiology of allergic asthma.