Treating chronic Pseudomonas infection of the bronchial tree is a very important part of the treatment strategy in patients with cystic fibrosis. There are only a few antibiotics which are effective against pseudomonas. Many of them soon lead to bacterial resistance (e.g. fluoro-quinolones). Inhaling antibiotics produces high sputum concentrations and low systemic toxicity. Tolerance is good and resistance rare. Several clinical studies, some of them doubleblind placebo controlled, have shown a positive effect of inhaled antibiotics on symptoms, on frequency of necessary i.v. therapies and also on pulmonary function. Most commonly aminoglycosides (tobramycin) and colistin, which is not yet registered in Switzerland, are used. The main indication is chronic therapy of Pseudomonas infection.