Cystic fibrosis (CF), the most common autosomal recessive disorder at least in western countries, is caused by mutations of the cystic fibrosis transmembrane conductance regulator molecule (CFTR) and affects approximately 40 000 patients in Europe. Most, if not all, CF-patients develop a chronic pulmonary infection with Pseudomonas aeruginosa (P. aeruginosa). At present it is un-known why CF-patients are highly sensitive to P. aeruginosa infections and, most important, no curative treatment for cystic fibrosis is available.