EBC collection is non-invasive method for obtain samples from the lower respiratory tract, which contains large number of biomarkers including isoprostanes, nitrogen oxides and hydrogen peroxide. The isoprostanes are a family of products from arachidonic acid produced by the non-enzymatic action of ROS. Increased blood level of 8-isoprostane is considered a reliable index of lipid peroxidation in vivo due to its chemical stability. NO. and superoxide anion (O2.-) react to form ONOO-, which is a powerful oxidant. Nitrites (NO2-) and nitrates (NO3-) are end products of nitric oxide (NO.) and peroxynitrite anion (ONOO-) metabolism and present in the epithelial lining fluid of the respiratory tract. Hydrogen peroxide (H2O2) is a ROS and volatile molecule produced from conversion of superoxide anion (O2.-) to H2O2 by superoxide dismutase and released from inflammatory and epithelial cells of respiratory system.