In this research work, the performance of the measurement system (TDLAS) has been improved, it was connected to the computer for acquisition and processing data using the programming language MatLab. The internal surface of the cavity was coated by paraffin wax, adsorption is significantly lowered. This system has been employed to measure the concentration of ammonia in exhaled breath for 20 healthy volunteers in two cases (fasting and non-fasting), and 36 volunteers with chronic renal disease (before hemodialysis).