Lung cancer is one of the few neoplasia in which the principal aetiology is known, with cigarette smoke donating a considerable oxidative burden to the lungs. This may be part of the aetiology of lung cancer, but the neoplastic process is also associated with increased oxidative stress. Nonetheless, it is difficult to study the mechanisms behind the induction of lung cancer in smokers, but newer techniques of breath analysis targeting markers of oxidative stress and anti-oxidant capacity show promise in unravelling some of the pathways. This review highlights recent developments in the assessment of oxidative stress by non-invasive methods of breath analysis which are becoming powerful research techniques with possible clinical applications.