It has been suggested that the delta F508 deletion, the most common mutation in the cystic fibrosis (CF) gene, might be linked to chronic bronchial hypersecretion. We investigated whether such an association could be found in chronic bronchitis, since chronic bronchial hypersecretion is an important and specific element of chronic bronchitis. We screened 100 patients hospitalized for chronic bronchitis with six of the most frequently occurring CF gene mutations: delta F508, R553X, G542X, G551D, N1303K, and 621-1G-->T. Only one patient affected by chronic bronchitis and diffuse bronchiectasis was heterozygous for the deletion delta F508; no other mutations were found. This is not significantly different from the expected frequency of CF carriers in northern Europe, which is 1 in 25. Thus, no association between the most commonly occurring cystic fibrosis genes and chronic bronchitis is likely to exist and routine screening of patients without further signs of cystic fibrosis would seem to be of no benefit in northern Europe.