Updated project metadata. The etiology of the inflammatory bowel diseases, including ulcerative colitis, remains incomplete, but recent findings points to the involvement of complex host-microbial interactions. We hypothesized that an analysis of the proteins on the host-microbial interacting surface, the intestinal mucosa, could reveal novel insights into the diseases. Mucosal colonic biopsies were extracted by standard colonscopy from sigmoideum from 10 ulcerative colitis patients from non-inflammed tissue and 10 controls. The biopsies were immediately following extraction snap-frozen for protein analysis and the protein content of the biopsies was characterized by high-throughput quantative gel-free proteomics.