Inflammation clearly contributes to the progression of cystic fibrosis (CF) lung disease. Anti-inflammatory therapy with alternate-day corticosteroids and twice-daily high-dose ibuprofen in patients with CF has shown clinical benefit, but adverse effects and other considerations have markedly limited their use. Therefore, alternative anti-inflammatory agents are urgently needed. Results from the clinical trials of alternate-day corticosteroids and high-dose ibuprofen in CF indicate that anti-inflammatory therapy will probably not result in improvement in pulmonary function, but will slow the rate of decline. This expectation imposes constraints on the design of studies to test new anti-inflammatory agents, requiring that they use many patients over a considerable period of time (years, rather than the months that are necessary to evaluate anti-infective or anti-obstructive therapies). Thus, it is highly desirable to design a strategy for evaluation of prospective anti-inflammatory agents that will allow for the selection of only the most promising agents for further study in Phase III type trials. Of additional concern is the fact that some pharmaceutical firms have not pursued development of anti-inflammatory agents for CF because there were no early indicators of efficacy. This presents an insurmountable hurdle for translation of research advances into clinical treatments. Some means of screening candidate drugs is urgently required. This study will assess the measurement of inflammatory mediators in induced sputum as one such strategy. The hypothesis to be tested is that ibuprofen will reduce neutrophils, active elastase, and pro-inflammatory cytokines in induced sputum after 4 weeks of therapy in patients with CF.