SummaryIn order to investigate the effects of airway cooling on bronchial responsiveness in normal subjects, we measured bronchial responsiveness to inhaled methacholine with and without the inhalation of cold air. Two out of seven subjects showed an increase in baseline respiratory resistance (Rrs) during cooling of the airway but the other five subjects showed little change in their baseline Rrs. All subjects increased bronchial responsiveness to methacholine. Additionally, the threshold dose of methacholine decreased to one‐third of the control dose with cooling of the airway. We speculate that airway cooling increased bronchial responsiveness to methacholine in normal subjects presumably due to increased vagal tone, increased alpha‐adrenergic activity and/or a release of chemical mediat