Considerable interest of specialists all over the world has focused on the measurement of the markers of inflammation and oxidative stress in the exhaled breath condensate in patients with asthma or chronic obstructive pulmonary diseases recently. Use of exhaled condensate is based on the hypothesis that aerosol particles exhaled in human breath reflect the composition of the bronchoalveolar extracellular lining fluid. The standard collection of the material requires condensation of exhaled air and the samples have to be kept in biologically inert containers. Measurement of the very low concentrations of selected substances requires very sensitive analytical methods. The examination of exhaled breath condensate is absolutely non-invasive method, which can be repeated as often as needed and it is extremely well tolerated both by children and seniors. Markers in the condensate enable detection and quantification of the inflammation process, the disease monitoring, and assessment of the response to the treatment. The breath condensate diagnostics is a new progressive method and in the patients with asthma and chronic obstructive pulmonary disease it can bring complementary information to the very sensitive method of determination of exhaled nitric oxide.