The aim of this study is to investigate whether the microbiota in the upper respiratory tract (URT) (nose, nasopharynx and sinuses) of chronic rhinosinusitis (CRS) patients is disturbed compared to healthy individuals. Therefore, bacterial DNA from swabs, aspirates and tissue will be isolated via commercially available DNA extraction kits, followed by Illumina MiSeq sequencing in order to identify the bacterial species present in these samples. Special attention will go to microbial species that are overrepresented in the healthy populations as potential health promoting microbes (i.e. probiotics). A better understanding of the URT microbiome might help us to better understand the pathology of CRS and might help to develop new microbiota-based strategies for CRS.