Lung disease in cystic fibrosis (CF) continues to be the major cause of morbidity and mortality, with the mechanisms whereby the biochemical defect causes lung disease receiving considerable attention. CF is caused by mutations in a 230 kB gene located on chromosome 7 which codes for the cystic fibrosis transmembrane conductance regulator (CFTR).¹ CFTR functions in the main as a cAMP regulated chloride channel in epithelial and glandular structures.² It has long been recognised that the abnormal chloride secretion by bronchial epithelial cells in CF predisposes to the development of bronchial damage and inflammation. The mechanism is under debate, but altered biochemical constituents of airway surface liquid,^3–5 function of the mucociliary escalator,⁶ and the function of antibacterial defence molecules such as defensins⁶ are all thought to play a part. What is less clear is whether inflammation itself can feed back to further compromise the abnormalities in chloride transport leading to an amplificatory cycle of lung destruction. Studies of nasal potential difference in patients with CF have shown that there is a range in the severity of chloride flux reduction. …