Bronchial hyperreactivity in cystic fibrosis and asthma.

We studied 113 patients with CF and compared their responsiveness to inhaled methacholine to that of 50 asthmatic children and 26 normal children. Positive responses to MCh occurred in 51% of the patients with CF and 98% of those with asthma. There was a significant correlation between a positive response to MCh in CF and poor pulmonary function. There was no relationship between allergic rhinitis or positive allergen skin tests and a positive MCh response. Dose-response curves and time course to MCh challenge differed in CF and asthma. Bronchial hyperreactivity is thus common in CF but is different from that in asthma.