The effects of environmental pollutants on human health and, in particular, on the respiratory apparatus, can be studied fundamentally by means of epidemiological and controlled exposure studies. One epidemiological study has reported the results of research which compared pulmonary function in adults with the average annual concentration of major pollutants in 8 geographical areas of Switzerland; the results demonstrated a direct relationship between atmospheric pollution and a worsening of pulmonary function. Controlled exposure studies, on the other hand, document the effects of specific air pollutants. Ozone (O3) is a secondary pollutant produced in the atmosphere by photochemical reactions which exerts a potent antioxidant and peroxidant action on biomolecules, whether intra or extracellular, with the production of free radicals. Nitrogen dioxide (NO2) is found mainly indoors due to its being a product of combustion of kitchen gas--it possesses low reactivity and low solubility that allows its penetration to the periphery of the lungs; the harmful mechanisms induced by NO2 are not well understood and could differ from those of O3. Sulphur dioxide (SO2) is found above all outdoors and is documented to affect the respiratory function of asthmatic subjects at concentrations above 1 part per million (ppm) while it has a doubtful effect on healthy subjects. Suspended particulate matter (SPM) is one of the major pollutants present in the air that comes mainly from vehicle exhausts, especially diesel models. Although the epidemiological data indicates a close relationship with both cardiac and respiratory pathology, the biological mechanisms by which it exerts its toxicity are still not well established. The great variability in individual response to pollutants suggests the need for further sensitivity tests to be carried out: it is of importance to identify specific genes with a stabilising role in cellular protection against oxidative stress, that influence the production of chemical mediators of inflammation.