18F-FDG positron emission tomographic (PET) scanning is a major imaging tool widely used to investigate lung function and lung disease. Tomographic imaging of drug delivered to the lung via the aerosol route can provide data that link the regional distribution and pharmacokinetics of a specific drug to clinical efficacy. Correlation with routine clinical functional measurements is possible, but, whereas 3D imaging data provides local drug deposition information, clinical tests of respiratory status are "black-box" measurements with outcomes specific to large or small airways inferred from the results. However, biopsies may be obtained directly from the tissue being imaged and therefore allow correlations with tracer uptake in the particular tissues. Imaging a radiolabeled pharmaceutic over time provides temporal information of receptor binding, drug absorption, or drug clearance from airways or the alveolar space. Changes in the deposition of inhaled aerosols within the lung related to the presence of disease or resulting from inhalation challenge interventions or inhaled therapies can be visualized with PET and may correlate with clinical outcomes. As well, the amount of an inhaled tracer deposited in various regions of the lung can give an indication of the efficiency of drug delivery and, combined with the regional distribution of the drug within the lung and the rate of drug absorption, estimate clinical efficacy and safety.