Abstract: S-carboxymethyl cysteine has been proposed for administration in nasal sprays, nasal drops or aerosols in otolyaryngology and in pneumology. When administered by the digestive route, this compound has the unexpected effect of reducing the viscosity of secretions of the respiratory tract. Administration to patients may be at a level of 1.5 to 3g per day in the form of a syrup, gelatine-coated pills or capsules, tablets or suppositories, in which other active materials, e.g., antibiotics, antihistamine drugs, corticoids or bronchodilators, may also be present.