Avoiding oxidative stress in the airways is important for the treatment of respiratory disease associated with gastroesophageal reflux disease (GERD). It is often difficult to decide whether GERD is causing airway inflammation or whether an airway disease is complicated by GERD. Measurement of exhaled breath condensate (EBC) is performed by cooling and collecting the airway lining fluid contained in exhaled air. A decrease of pH and an increase of the 8-isoprostane concentration in EBC have been observed in patients with mild to moderate asthma accompanied by GERD. There are still problems to be overcome before EBC can be used clinically, but pH and 8-isoprostane may be promising objective markers of airway inflammation due to GERD. The disease concept and diagnosis of GERD are constantly advancing, including the development of impedance methods. It is expected that treatment will be based on the latest diagnostic knowledge of GERD associated with respiratory disease and on monitoring of airway inflammation.