Acetylcysteine is a mucolytic agent that reduces the viscosity of secretions probably by the splitting of disulphide bonds in mucoproteins. Moreover it gives antisecretory effect. These results in clearing of respiratory ducts and facilitate breathing. Acetylcysteine also has anti-oxidant properties by reacting with free radicals and also by serving as a precursor to glutathione, which is an important intra and extra-cellular antioxidant. By providing anti-oxidant action, it neutralizes exogenous and endogenous oxidants, which in fact act as pathogens in respiratory inflammations.