Pulmonary Exacerbation Cohort  Inclusion Criteria:  Diagnosis of CF (: a. One or more clinical features of CF AND (b or c); b. Sweat chloride > 60 mEq/L; c. Two known CF mutations) 3 or more admissions with an admitting diagnosis of pulmonary exacerbation, requiring IV antibiotics, within the 12 month period prior to study enrollment.  Clinically Stable Disease Cohort  Inclusion Criteria:  Diagnosis of CF (: a. One or more clinical features of CF AND (b or c); b. Sweat chloride > 60 mEq/L; c. Two known CF mutations) Age and gender matched to Pulmonary Exacerbation Cohort No hospitalizations with an admitting diagnosis of pulmonary exacerbation, within the 12 month period prior to study enrollment.  Exclusion criteria for both groups includes:  History of intolerance or inability to tolerate the induced sputum protocol. History of organ transplantation. Any patient that in discretion of the investigators is not suitable. Any clinically unstable participants.