Oxides of nitrogen including nitric oxide (NO) are gases present in atmospheric air, and have been considered as air pollutants derived predominantly from automobile exhaust and domestic gas cookers. Indeed at one stage NO was considered as a potential toxic lethal contaminant of ‘nitrous oxide cyliders used in anaesthesia (1). However, following the independent identification of the endothelium-derived relaxing factor (EDRF) by Palmar et al. (2) and Ignarro et al. (3) in 1987 as nitric oxide, and the subsequent recognition of the L-arginine:NO pathway (4,5), NO was named molecule of the year by Science in 1992. Since then a considerable body of research has been conducted to characterize the regulatory role of NO in various organ systems in animals and humans, in both health and disease, and it is now appreciated that NO has a potential involvement in a number of aspects of respiratory physiology and pathology. The intention of this review is to integrate the recent advances in this rapidly growing field.