This thesis describes and discusses oxidants and anti-oxidants and their relation to human disease. Cigarette smoking is used as the model for the study of chronic inflammatory processes, firstly, to establish a causative link between oxidants and disease viz. lung function abnormalities in smokers, secondly to evaluate the interaction between hyperactive phagocytes and anti-oxidant defences and thirdly, to investigate the possibility that intervention with anti-oxidants may ameliorate the effects of chronic inflammation.