When we exhale, we breath out several thousands of molecules with a diverse range of concentrations. However, when we have any disease or metabolic disorder, or any kind of bacterial infection, the profile and excretion kinetics of these exhaled molecular constituents change. Their concentrations may also change from the normal levels. Some of these molecules or their specific isotopes may be associated with the pathogenesis of the disease and can be markers of the particular medical conditions. Consequently, when our health changes, breath analysis may provide an alternative, rapid and non-invasive diagnostic method.