Cigarette smoking is the major factor responsible for chronic obstructive pulmonary disease (COPD). COPD occurs in a minority of smokers, but the host factors that modify risk of disease have not been clearly elucidated. There is significant clinical and histopathologic overlap between COPD and asthma, including the accumulation and activation of airway inflammatory cells. These two disorders are compared and contrasted. Abnormal airway inflammatory cytokine expression in these disorders is discussed.