After a brief review concerning NO biosynthesis, distribution and actions, its main normal and pathological implications are presented. The NO modulatory role on the bronchiolar and vascular smooth muscle basal tone, as well as its involvement in local inflammatory reactions are shown. Physiopathological broncho-pulmonary NO implications are completed with data concerning its inhalatory use in the treatment of pulmonary arterial hypertension, acute respiratory distress syndrome and severe pneumonia.