Collecting exhaled breath condensate (EBC) has become a frequently used method in respiratory researches to date. Through this method we can sample airway surface liquid non-invasively by streaming the exhaled breath through a cooled chamber and after we examine the fluid deposited on the wall of the condenser. The sample contains several mediators, biomarkers. The pH of the condensate is one of the most important markers measured in the EBC. Measuring the pH is easy, cheap and it is in the optimal range, there is no problem with the detection limit. The uncertainty of the pH assays is derived from the instability of the EBC pH which results from the altering carbon-dioxide concentration. Many articles have been published on EBC pH in different airway diseases. Acidification of the condensates has been described in bronchial asthma (especially in acute exacerbations), chronic obstructive lung disease (COPD). Due to the steroid treatment the pH has increased in both cases. In patients with bronchiectasis, cystic fibrosis and in chronic cough (bronchial asthma, gastro-esophageal reflux, postnasal drip, and unknown origin) the pH of EBC was also lower. Acidification of the airways in different diseases can play a role in the pathomechanism, and its indicator, the EBC pH might help managing patients with airway diseases.