Lung disease such as asthma and chronic obstructive pulmonary disease (COPD) are increasing the global heath burden affecting hundreds of millions of people worldwide. The development of novel inhaled therapies is being hindered by the lack of understanding of alveolar macrophages to inhaled particulate medicines. In animal models, there is increasing evidence that inhaled medicines are taken up by alveolar macrophages resident within the lung resulting in poorly understood perturbations. The aim of this work is to identify an appropriate in vitro alveolar macrophage culture model for the generation of a human co-culture model. This model will allow us to better understand alveolar physiology at a cellular level and predict in vivo responses to pharmaceutical particulates. Human lung, U937 monocyte cell line was differentiated to alveolar macrophages in the presence of phorbal myristate acetate (PMA) and differential characteristics specific to PMA naïve and PMA treated cells were identified. These characteristics include cell viability, immunological changes in surface markers and phagocytic activity. Human U937 monocyte cell line was differentiated to the macrophage phenotype using (5 – 500 nM), incubation and resting times (0 – 72h). Cells were harvested and differentiation was validated for surface marker expressions by microarray technology, flow cytometry and confocal microscopy. In general, cellular perturbations were identified in alveolar macrophages compared to their phenotype. The U937 cell line has the potential to provide a platform appropriate to explore macrophage responses. Characterisation of a cell line representative of alveolar macrophages will allow for a concrete basis to be established for which a co-culture model can be developed in order to understand alveolar macrophages in response to inhaled pharmaceuticals. Work is ongoing to standardise a protocol for generating alveolar macrophage cells from monocytes and to validate the U937 cell line as a suitable inhaled response model.