In some people exposed to the long‐lasting activity of compounds contained in the “ chimney trail “ of power station the increasel level of MetHb was found but no increased values of SHb were observed Human organism responds to low concentrations of nitrogen oxides contained in the atmosphere by reaction to increased level of MetHb as well as the increase of GSH concentration in erythro‐cytes found near the upper limits of norm, and the increase of activity of G‐6‐PD and first of all the activity of MetHb‐Red. In the examined cases the Hb moleculary structure was of A type≪ The mechanism of human organism's response to the low concentrations of nitrogen oxides in inhaled air may be examined in two aspects, namely as the subtoxic effect with the increase of MetHb and as hormetic activity, stimulating the increase of reduction system activity.