Patients with cystic fibrosis will be asked to participate in this study by undergoing standard medical tests and procedures. Patients will have a history taken and have a physical examination as well as blood tests, and a sweat test (a test for cystic fibrosis of the pancreas in which electrolytes are measured in collected sweat). Patients may also be asked to provide samples of urine, stool, and sputum for additional tests. More complicated procedures such as bronchoscopy or bronchoalveolar lavage may be required for diagnosis, treatment, or research purposes.