The Cl− concentration of trachea and main stem bronchi airway surface liquid (ASL) of CF patients has been measured at around 129 and 170 mM respectively (compared to 84 and 85 mM for normal ASL).67 In CF patients, it has been demonstrated that the activity of AMPs is much lower in the ASL of CF patients compared to normal ASL.67,68 As many AMPs have been shown to be salt-sensitive in vitro (that is, they display lower activity in higher salt concentrations), it is believed that this could be the reason for their lack of efficacy in CF patients.69 The gene discussed is ADSL; the disease is cystic fibrosis.