Methods: This is a cross-sectional diagnostic / mechanistic protocol to investigate airway host-defenses. The patient populations for these studies include individuals with recurring airway infections such as those with nontuberculous mycobacteria lung disease who may have defective airway host defenses as a predisposing factor, individuals carrying a tentative diagnosis of the three known genetic disorders of mucociliary clearance (PCD, variant CF, or PHA), and individuals suspected to have one of these disorders but with inadequate or inconclusive diagnostic tests. Individuals in this latter category must have a preliminary clinical evaluation to evaluate for other more common disorders that may have similar manifestations including classical CF, immunodeficiency, asthma, and severe gastroesophageal reflux. The evaluation will include a detailed assessment of clinical features; specialized laboratory measurements such as nasal potential difference to evaluate the function of chloride and sodium channels associated with CF and PHA, nasal biopsy specimens and nasal nitric oxide measurements to assess cilia structure and function which are abnormal in PCD; and genetic studies to identify disease - causing mutations in genes associated with CF, PCD, and PHA.