The diagnostic accuracy of colonoscopy depends on the quality of the preparation. The adequacy of the preparation determines whether complete visualization of the mucosa and identification of pathologic lesions is achieved. For reasons that are not entirely clear, colonoscopies scheduled in the afternoon have been identified as a risk factor for having an inadequate preparation. Standard bowel preparation regimens at BMC include polyethylene glycol- electrolyte solutions (PEG-ELS) in full (four liters) and reduced (two liters) forms. These laxatives are typically administered either the evening prior to the colonoscopy or in "split dose" (a portion the evening before and a portion the morning of the colonoscopy). The percent of failed colonoscopies due to a fair/poor preparation in our endoscopy unit is 17-20%. Our trial seeks to establish the efficacy and safety of a reduced volume PEG-ELS laxative given on the day of the colonoscopy.