In the period of 1982-1990 a total of 5760 children (2893 boys, 2816 girls) were examined in the frame-work of the Clean Air Programme Rhine-Main: from the polluted Rhine-Main area 2511 children (Wiesbaden 1682, Frankfurt since 1985, 825), from the control areas 3153 children (Freiburg area 1937, Starnberg area 1316). Healthy children living in the industrialised Rhine-Main area exhibited alterations of the following parameters compared with healthy children living in the less polluted control areas: Long-term alterations, enlarged and fissured, rough palatine tonsils, palpably enlarged cervical and mandibular lymph nodes, Short-term alterations, erythrocyte count: from 1981-1988 relatively smaller numbers, from 1988-1990 equalized to the scatter range of controls, hemoglobin values: corresponding to erythrocyte counts, activity of lymphocyte nucleoli: increased until 1985, later on equalized, lymphocyte count: reduced, T8-suppressor cell count: decreased, chemiluminescence of granulocytes: increased, palatine tonsils: altered microbial contamination with contact germs, altered physiological resident flora, heavy metals (Pb, Cd) in hair: from 1982-1990 increased, then slowly reduced corresponding to the results of the ambient air analyses. These findings indicate an increased inclination for reaction of the healthy juvenile organism in the sense of biological adaptation to long-term stress, i.e. living for years in an area with air pollution, and are also in good agreement with the measuring values characterising the ambient air quality.