Fiberoptic bronchoscopy and associated techniques of airway sampling have contributed immensely to our understanding of asthma pathogenesis. The major advance of investigative bronchoscopy has been the ability to obtain information that is not readily available by other monitoring methods in asthmatics. The current paradigm of asthma, a chronic inflammatory airway disorder, has been strongly supported and advanced by the study of mild asthmatics by investigative bronchoscopy. Bronchoalveolar lavage, airway mucosal brushing, endobronchial biopsy, and measurement of airway gases have been performed in mild asthmatics to further characterize the nature of inflammation with experimental challenge procedures as well as with various anti-inflammatory therapies. This article reviews the following issues: general guidelines from several workshops and the relative safety of bronchoscopy in asthma research; technical issues related to specimen retrieval and processing; and data obtained from studies that have used bronchoscopy for investigation of stable asthma, asthma with allergen provocation, or asthma treated with anti-inflammatory therapy.