Breath analysis is at best in screening, in very specific applications (where there are no other good tests), in therapeutic monitoring (therefore following only relative changes), monitoring exogenous gases (bacterial emissions or poisons), in tests where certain gases are metabolised (inside the body) on purpose by using some precursor molecule or in any real-time tests. Real-time monitoring of exhaled gases (therapeutic monitoring, toxicology, occupational health). A new detection method for ammonia in high concentration of CO2 and H2O is reported, which uses a wavelength modulated photo acoustic spectrometer based on a near-infrared tunable erbium-doped fiber laser in combination with an optical fiber amplifier. The problem of ammonia detection in high concentration of CO2 and H2O is resolved at atmospheric pressure. Together with a special algorithm processing, the minimum detection limit is improved from 16 ppb (signal to noise ratio = 1) to 2 ppb((signal to noise ratio = 1/886) in simulated breath samples (5.3% CO2 and 6.2% H2O (100% relative humidity at 37°C)).