Clinical and translational research in cystic fibrosis (CF) is hampered by a lack of biomarkers that can be used to identify promising new therapies. There is an urgent need for development and validation of biomarkers that more quickly predict the usefulness of potential drugs in CF and might prognosticate clinical course. In particular, combinations of protein biomarkers that can be obtained non-invasively offer great promise. The goal of this project is to determine whether protein biomarkers in blood can demonstrate a beneficial effect of treatment over two weeks. We intend to initially target an acute pulmonary exacerbation in CF because we know that subjects being treated with intravenous antibiotics and enhanced mucus clearance display clinical improvements within two weeks. We propose to prospectively collect blood samples from a large cohort of well-characterized CF persons serially during inpatient admissions for a pulmonary exacerbation and longitudinally during annual visits. Through this proposal, we hope to identify a CF lung injury biomarker panel that increases in the setting of an acute pulmonary exacerbation and improves rapidly following intravenous antibiotic therapy. Additionally, we will begin to explore whether this CF lung injury biomarker panel might also prognosticate clinical course including decline in pulmonary function. Finally, this study will serve as an important source of blood samples that will be banked for future biomarker and therapeutic studies designed to benefit the entire CF community.