This invention deals with a therapeutic process of the drug, bio-affecting and body treating composition type.  More particularly, it is concerned with the crystalline ammonium salt of N-acetyl-L-cysteine and its use in a process for effecting mucolysis of pulmonary secretions. 
N-acetyl-L-cysteine is a known pharmaceutical and has been used with considerable success as a mucolytic agent, refer to U.S. Pat.  No.  3,091,569.  It has also been described as being of value in ameliorating inflammatory conditions in mammals (U.S. Pat.  No.  3,591,686) and in permanent deformation of human hair (U.S. Pat.  No.  3,242,052).  The use of N-acetyl-L-cysteine in the treatment of pathological disorders in the respiratory system such as cystic fibrosis is a well-developed medical practice.  N-acetyl-L-cysteine is also of value in the treatment of chronic bronchopulmonary disease including chronic emphysema, emphysema with bronchitis, chronic asthmatic bronchitis, tuberculosis, bronchiectasis, primary amyloidosis of the lung and in the treatment of acute bronchopulmonary diseases such as pneumonia, bronchitis, tracheobronchitis.  The patents cited hereinabove disclose the preparation of various salts of N-acetyl-L-cysteine by neutralization with suitable alkaline-reacting substances such as sodium hydroxide, ammonium hydroxide or the like.  The salts are prepared in situ and are not isolated or characterized.  Certain salts of N-acetyl-L-cysteine such as the sodium salt and the like have been isolated and characterized by T. A. Martin, et al.,  Journal Medicinal Chemistry, 11, 625 (1968). 
For mucolytic purposes N-acetyl-L-cysteine has been administered heretofore by nebulization, direct application, or intratracheal instillation in the form of a solution of the sodium salt.  The use of finely divided solid N-acetyl-L-cysteine for inhalation, i.e. insufflation, via a dispenser in which the N-acetyl-L-cysteine is dispersed into an air stream by fluidization technique wherein the principal source of energy is the inspiratory action of the inhaler is described in U.S. Pat.  No.  3,634,582.  However, administration of N-acetyl-L-cysteine by this method is not entirely satisfactory in that it produces severe coughing and irritation.