CFTR functions as an epithelial chloride channel, and it has been suggested that altered water absorption may change the composition of the mucus present on the epithelial cells of the respiratory tract in cystic fibrosis lungs, resulting in reductions of mucociliary clearance, the function of defensins, and the ability to eliminate P. aeruginosa (2). This evidence concerns the gene CFTR and cystic fibrosis.