The Institute of Hygiene at Rostock initiated studies in 1980 on schoolchildren (1st to 4th form) in air-hygienically differently affected areas of the former GDR, as well as studies on probationers of the same age in non-polluted areas. The spectrum of methods included besides clinical, sensorial and psycho-diagnostical investigations, also haematological, immunological and pulmonary functions tests. The results indicate that the state of health of children living in industrial areas is impaired. After a recuperating for four weeks under clean air conditions the changed values were normalised and adapted to the values of the non-exposed control group. The long-term effect of the recuperating stay lasts for 9 months.