Longitudinal Observational Study of Severe Asthma

Background: \- Asthma is a lung condition that causes difficulty breathing and decreased lung function. Some people with asthma have more severe disease symptoms. They may be less responsive to standard treatments such as steroids. Researchers want to compare severe asthmatics with mild or moderate asthmatics or people without asthma over a long period. This information may help identify new treatments for people whose asthma is not well controlled by standard medications. Objectives: \- To compare severe asthmatics with mild or moderate asthmatics, and healthy volunteers, to study the progression and outcomes of the disease. Eligibility: * Individuals at least 18 years of age who have been diagnosed with asthma for at least 1 year. * Healthy volunteers at least 18 years of age. Design: * This study will involve an initial visit to the NIH Clinical Center for all participants. Selected participants may be asked to return for repeat visits over a number of years. The test results from participants with asthma will be compared with those from the healthy volunteers. * All participants will be screened with a physical exam and medical history. * Participants may (but will not necessarily) have the following tests at each visit: * Complete medical history and physical exam * Blood, urine, sputum, and nasal cell samples * Breath tests and heart and lung function tests * Six-minute walk test to measure ability to exercise * Imaging studies such as chest x-rays, bone density scans, and sinus scans * Allergy skin testing * Vocal cord exam * Overnight sleep study * Participants may remain on the study for as long as they are willing to participate and do not develop health problems that will interfere with the study.