The Aerocrine exhaled nitric oxide (NO) monitoring system NIOX was cleared by the US Food and Drug Administration for clinical application in patients with asthma in May 2003. The fractional concentration of exhaled NO has been extensively researched as a marker of airway inflammation in asthma and other diseases and is now poised to enter clinical application. The American Thoracic and European Respiratory Societies' current guidelines recommend measurement at constant expiratory flow, which is difficult for some adults and children. The NIOX NO monitoring system was designed to facilitate standardized measurement according to guidelines. A clinical study was performed together with in vitro testing to obtain clearance. Exhaled NO levels were measured in unstable steroid-naive adult and pediatric asthmatic subjects and again after a 2-week treatment with inhaled corticosteroids. Exhaled NO levels decreased highly significantly, with 95% confidence limits for the decrease of -40% to -60% accompanied by clinical improvement. This trial, together with extensive in vitro testing, led to the clearance of NIOX by the US Food and Drug Administration. This article in the journal's "New products" feature section will describe background material regarding exhaled NO, special features of the NIOX NO monitoring system, and how this tool can be incorporated into clinical asthma management.