The purpose of this study is to assess treatment responses comparing a newly FDA-approved PEG laxative versus placebo.

Inclusion Criteria:

• Adult male or female ambulatory outpatient age 19 or older.
• Patients meet ROME II Criteria
• Patients not meeting ROME IBS criteria
• Use of a constipating medication (>= 3% in PDR)
• If female and of childbearing potential, patient must be surgically sterilized or using oral contraceptives, depot contraceptives, intrauterine device, or testifies that she is monogamous with a vasectomized partner, or practices abstinence and will continue to do so during the duration of study
• Written informed consent.

Exclusion Criteria:

• Known or suspected obstruction, gastric retention, ileus, perforation, fecal impaction or inflammatory bowel disease.
• Prior small bowel or colonic resection or colostomy.
• Weight < 80 lbs.
• Unwilling or unable to undergo any colon diagnostic examinations at the end of the study if not performed within 5 years of the informed consent date advised by clinically accepted indications.
• Positive stool hemoccult.
• Significant cardiac, renal or hepatic insufficiency.
• Pregnant or expecting to become pregnant within 120 days of study enrollment.
• Lactating or breast feeding.
• Subjects who in the opinion of the investigator would be unable to comply adequately with the study plan.
• Use of investigational drugs in the last 30 days.
• Patients with known allergy to PEG or PEG medications such as PEG or sulfate-free electrolyte lavage solutions