Background: The dysregulation of airway pH control may have a role in asthma pathophysiology. The measurement of exhaled breath condensate (EBC) pH and ammonia levels may be used as a noninvasive method to study acid–base status in the airway of asthmatics. Methods: Exhaled breath condensate from 29 allergic stable asthmatic children and 13 healthy controls was collected by cooling exhaled air during tidal breathing. Ammonia was measured by high-performance liquid chromatography with fluorescence detection. pH was measured after deaeration of EBC samples by bubbling with argon. The children also underwent FENO measurement. Results: Both pH and ammonia values in EBC were significantly lower in the asthmatics than in the control group [pH: ICS-treated (median and interquartile range) 7.70 (7.62–7.74), steroid-naïve 7.53 (7.41–7.68), controls 7.85 (7.80–7.90), P < 0.01 and P < 0.001, respectively; ammonia: ICS-treated 476.17 M (282.50–594.80), steroid-naïve 253.24 M (173.43–416.08), controls 788.30 M (587.29–1310.39), P < 0.05 and P < 0.001, respectively]. Both pH and ammonia values were higher in ICS-treated than in steroid-naïve asthmatic children. There was a significant correlation between EBC pH and ammonia concentrations. Conclusions: These data show that EBC pH values of stable asthmatic children are lower compared with those of healthy controls and positively correlated with ammonia concentrations, supporting the hypothesis that airway acidification may have a role in the pathobiology of allergic asthma.