Inclusion Criteria:  Patients referred for out-patient colonoscopy as a result of positive hemoccult. Patients able to read and understand danish. Patients able to give informed consent. Patients of Scandinavian ethnicity.  Exclusion Criteria:  Previous large bowel resections Suspicion pre or intraoperatively of benign or malignant disease of the colon Known inflammatory bowel disease. Immuno-modulation treatment Chemotherapy. Daily smoking > 21 weekly units of alcohol < 18 years of age