As a mucolytic in respiratory disorder associated with the production of viscous mucus such as acute and chronic bronchitis. In alveolar protenosis to remove proteinaceous material by repeated lavage with heparin and acetylcysteine which may prolong survival up to 5 years. During mechanical ventilation in premature infants to relive severe recurrent atelectasis. In adult respiratory syndrome acetylcysteine is given intravenously.