The most useful investigation for profuse lower gastrointestinal bleeding is

.Indications for colonoscopy includes * Bleeding per rectum, resistant anaemia. * To take biopsies from different pas of the bowel. * To identify synchronous growths, ulcerative colitis. * To remove polyps. * When barium enema shows irregularity. * For therapy--colonoscopic polypectomy, dilatation of stricture colon, fulgaration. Contraindicated in Acute ulcerative colitis. ref:SRB&;s manual of surgery,ed 3,pg no 891