Radiotherapy of tumors in the pelvic region is increasing used, e.g. gynaecologic, rectal and bladder cancer. Reaction in surrounding healthy tissue includes an acute inflammation followed in many instances by fibrogenesis causing strictures. The reaction in abdominal organs to radiotherapy is strong, since the inflammation is sustained by leakage thorough a deranged bowel wall. This project aims at the study of interaction between gut bacteria, bowel integrity and tissue damage. Since radiotherapy is invariably used electively preventive measures are of interest to reduce damage to organs unaffected by cancer growth, such as the gut.