The aim of this study was to establish a relationship between bronchial hyperreactivity to carbachol and reflex bronchomotor response to the activation of cold receptors in the nose, and also to examine whether any differences exist between asthmatic patients with or without symptoms of rhinitis. The changes in interrupting resistance (Rint) induced by nasal eupnoeic inhalation of cold (-5 degrees C) dry air were measured in 22 normal subjects and in 18 asthmatic patients (nine of whom had asthma with rhinitis and nine without) with bronchial hyperreactivity to carbachol. In normal individuals, nasal cold air challenge induced a significant increase in Rint (+31%). This was also the case in asthmatic patients (asthma with rhinitis +49%; asthma alone +40%), but the increase was not significantly larger than for normal individuals. The magnitude of Rint increase induced by nasal cold air breathing was correlated with the sensitivity to carbachol (defined as the dose inducing a 50% increase in specific airway conductance (D50)) in asthmatic patients with symptoms of rhinitis. These observations suggest that airway hyperreactivity is associated with enhanced bronchoconstrictor response to the activation of nasal cold receptors, particularly when rhinitis is present.