Quality control and assurance are very important issues for multicenter clinical investigation. Although such investigation usually states that those factors are part of the investigation, at best this occurs to a minimal extent. Indeed, to ensure the best possible investigatory results with the least amount of variance between centers, the Asthma Clinical Research Network (ACRN) instituted strict written criteria that were continually overviewed. This article describes the ACRN's quality control of: clinic procedures and equipment, training and certification of study personnel, site visit evaluations, and the procedures of bronchoscopy and sputum induction. The examples given in this report demonstrate how various aspects of our investigation are performed.