Irritable Bowel Syndrome (IBS) touches up to 10% of the population and is characterized by recurrent abdominal pain and disturbed bowel habits. We have established that Trypsin-3 is the most active protease in tissues from IBS patients. It augments epithelial permeability, causes pain reproducing IBS symptoms. Our aim is to identify key compounds for IBS drug development, based on Trypsin-3 inhibition. We propose 1/ to establish screening assays for specific Trypsin-3 inhibitors 2/ to screen two libraries, and 3/ to develop an ELISA kit as a companion tool for biomarker studies and possible patient stratification. With these approaches, we believe that we would establish the necessary conditions for Trypsin-3 inhibitors drug discovery. Our tools would not only definitively confirm the therapeutic potential of Trypsin-3 inhibition, but they will also constitute the basis for Trypsin-3 drug development.