There is a general consensus that continuous inhalation of air polluted with ozone is detrimental for the lungs and vital organs. Even if the concentration of tropospheric ozone is slightly above the tolerated dose, toxicity ensues owing to the cumulative dose inhaled for months. However, in medicine ozone is used as a real drug and a precise concentration and therapeutic dosage must be calibrated against the antioxidant capacity of blood. As ozone reacts with blood, it generates pharmacological messengers such as H(2)O(2) and lipid oxidation products (LOPs). These activate several biochemical pathways in blood cells, which after reinfusion are responsible for therapeutic activities lasting several days. Neither acute nor chronic toxicity has been registered.