 This is a randomized, controlled, parallel group, assessor-blinded study to compare two colon cleansing preparations for colonoscopy. Subjects meeting all inclusion and exclusion criteria will be randomized and assigned to one of two study groups: Group I PicoPrep or Group II Mannitol. In Group I, subjects will take one sachet of PicoPrep on the day before colonoscopy, and another sachet on the day of colonoscopy. In Group II, subjects will take Bisacodyl on the day before colonoscopy, and Mannitol on the day of colonoscopy. 