Classical methods of respiratory diagnosis were extended with methods allowing determination of the metabolic products from lung tissue – the biochemical analysis of expired air. Hydrogen peroxide is one of the substances used as markers of pathological processes in the respiratory system. This review describes position of hydrogen peroxide in the metabolic pathway of reactive oxygen species, methods of hydrogen peroxide measurement in expired air and changes in hydrogen peroxide production in lung diseases.

        Key words: oxidative stress, respiratory diseases diagnostics, reactive oxygen species, hydrogen peroxide.