Acute and chronic lung diseases are almost invariably associated with some degree of inflammation. Cells that evolved as an effective mechanism to counter infection and heal lung tissue may, in some circumstances, themselves be partially responsible for the pathogenesis of chronic lung disease that leads to irreversible lung damage and loss of lung function. Although standard measurements of lung function can document the progression of disease, the contributions of the numerous interacting elements to the process are difficult to measure in life. The use of molecular imaging techniques allows the different components of the inflammatory response to be monitored in situ in humans. In particular, positron emission tomography of selected markers targeted to specific cells and biochemical pathways can provide accurate measurements of disease activity, enabling a better understanding of inflammatory processes at all stages of disease. The practicability of sequential measurements allows one to monitor the natural history of different lung diseases. More importantly, imaging provides a unique tool for quantification of the modulation of discrete and specific aspects of inflammatory lung disease by targeted interventions. This should facilitate the development of new treatment strategies with better specificity for key elements of each disease.