Furosemide (frusemide) is mainly employed as a powerful diuretic that inhibits Na and K reabsorption in renal tubules. However other valuable pharmacological effects have been discovered that include a protective action from bronchospasm. The effects of furosemide on airways have been recognized to be more and more complex as far as an increasing amount of studies have been produced on this subject. The drug shows no acute bronchodilator effect, but prevents or attenuates bronchospasm caused by many factors, such as hyperpnea, drugs (metabisulphite, bradykinin, AMP), physical agents (hypo- and hypertonic aerosols), and allergen challenge in asthmatic patients. Furosemide is also active on upper airway mucosa, on which the drug decreases nasal resistance in patients affected by non-allergic rhinitis and exhibits a protective effect on nasal mucosa reactivity to the specific allergen in atopic subjects. The mechanism of action of furosemide on airways has not yet been fully cleared and interference with electrolyte epithelial transport, prostaglandins, inflammatory cell activity, vascular and neural regulation has been hypothesized. The interest for clinical application of inhaled furosemide has grown in last years. Some Authors have investigated whether the drug is effective in acute asthma attacks or not. Furosemide is one of the drugs currently used to prevent exercise-induced asthma. More recently, inhaled furosemide has been observed to decrease the sensation of experimentally-induced dyspnea. Apart from possible therapeutic application, studies about furosemide effects on respiratory mucosa can contribute to better understand the physiology of upper and lower airways.