During recent years there has been a growing interest in using non-invasive biomarkers to understand and monitor the airway inflammation in subjects with respiratory tract disorders. To date, the best validated and performing non-invasive biomarkers are measures of inflammation in induced sputum in both cellular and fluid phase, which can provide biological insights into the pathogenesis of respiratory diseases such as asthma and chronic obstructive pulmonary disease. The purpose of this review is to examine the principal literature on the different markers of inflammation in pulmonary diseases assessed by induced sputum analysis in either cellular or fluid phase.