This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. There has been much recent interest in the use of azithromycin in patients with CF who are chronically infected with P.aeruginosa. Three randomized, placebo-controlled trials have shown an improvement in lung function with 3-6 months of treatment. Most of the subjects enrolled in these trials were greater than or equal to 18 years of age and the majority had chronic infection with P.aeruginosa. Thus, there are limited safety data on prolonged use of azithromycin in young children with CF and limited efficacy data in patients with CF who are not chronically infected with P.aeruginosa. Some of the hypothesized mechanisms of action suggest that azithromycin could benefit CF patients who are not infected with P.aeruginosa.