The MEMORY trial is the first to primarily evaluate the effect of mepolizumab treatment on pulmonary function in patients with severe eosinophilic asthma. Importantly, using spirometry and bodyplethysmography will allow to evaluate additional parameters beyond FEV1 that more closely mirror the pathophysiological changes and functional aspects of airflow limitation in asthma in real life, e.g. airway resistance, hyperinflation and diffusion capacity. The proposed trial will answer the important questions: if, and if so, which parameters of airway (patho-) physiology as assessed by bodyplethysmography best reflect clinical response to mepolizumab therapy in patients with severe eosinophilic asthma. In addition, the time course to clinical response will be assessed. Equally important, there is only a loose correlation between FEV1 and parameters of asthma control and asthma-related quality of life. This is why another new and important aspect of this trial is to carefully monitor asthma control and asthma quality in life in correlation with lung function changes beyond FEV1. Finally, it is tempting to speculate that the proposed trial will contribute to the question how to best define clinical response to mepolizumab.