The aim of this research was to evaluate the response to aerosol antibiotic therapy in Cystic Fibrosis (CF) patients, who because of severe lung disease, were obligated to frequent hospitalizations to undergo intravenous antibiotic therapy. Ten patients, aged 2 to 20 years were submitted to 4 months cycles of aerosol antibiotic therapy for a total of 18 cycles. The daily treatment consisted of carbenicillin 1 g b.d. and gentamicin 80 mgs b.d. At the end of treatment there was a statistically significant improvement of the modified Huang score and of single clinical parameters such as body growth, apetite, physical activity, clinical thoracic evaluation, appearance of sputum. Almost all of the radiographic items remained unchanged: in only 4 cases there was an improvement of the atelectasis-broncopneumonia type lesions. Regarding lung function, there was a statistically significant increase of maximum midexpiratory flow rate (MMEF) from 40% predicted before treatment to 50% predicted after. The reduction of residual volume (RV) from 270% predicted before 170% predicted after treatment was quantitatively more important. Furthermore, the treatment brought about a drastic reduction in number of hospitalizations: from an average of 1,7 hospitalizations/year before to an average of 0,3 hospitalizations/year during treatment. The increased number of isolations of isolations of candida albicans is the only report which favors possible adverse effects, in particular the possibility that this type of treatment favors lung mycosis.