 Patients who are admitted with bleeding from their rectum and a negative endoscopic exam of the stomach and upper intestine are randomized like flipping a coin to receive a colonsoscopy either as an emergency within 12 hours or as a routine procedure 36 hours after admission. Patients are followed during their hospitalization to see if they have further bleeding, if they require blood transfusions, if they need other diagnostic tests, if they need surgery or other treatments, and how long they stay in the hospital. 