Nitric oxide is an endogenously produced gas with a wide range of biological effects and has been implicated in many physiological and pathophysiological processes. It is released by many cell types in various organs but is particularly important in the maintenance of normal lung function. Nitric oxide in exhaled breath has been identified as a marker for lung disease in some patients. Thus, it is appropriate to consider the lung separately for the role and functioning of nitric oxide. The authors identify key areas in the history, biochemistry, physiology, pathophysiology, immunology and...