: In several studies comparing of sodium phosphate solutions versus PEG, both regimen had similar efficacy of bowel cleansing and sodium phosphate solutions are more acceptable to patients because patient are required to consume smaller volume. But sodium phosphate solutions are associated with fluid and electrolyte disturbances, so use of sodium phosphate solution in routine medical check-up of outpatients is problematic. PEG can provide a rapid peroral approach to colon lavage without causing fluid and electrolyte disturbance. However, the need to ingest a large volume of fluid reduces patient compliance, and results in suboptimal bowel preparation. In order to overcome this disadvantage, several studies proved that split dose of PEG regimens were better quality preparation and more acceptable than single dose regimens. In Korea, need for outpatient or screening colonoscopy without laboratory test is increasing and split dose of PEG is used more frequently than other country in bowel preparation because of safety. But, superiority of split dose of PEG to sodium phosphate solution has not been demonstrated. The study was not yet existed about comparison of split dose PEG solution with sodium phosphate solution for bowel cleansing and tolerability in colonoscopy preparation. To use split dose of PEG in bowel preparation with medical evidence, we want to demonstrate split dose bowel preparation with PEG compared to sodium phosphate solutions provide a better colon cleansing efficacy and similar tolerability.

Study design: Investigator-blinded, prospective, randomized controlled trial

Subjects

1. Entry criteria: Adult outpatients(at least 18 years of age, under 65 years) who undergo scheduled colonoscopy for screening, cancer surveillance or want procedure with/without non-specific gastrointestinal symptoms.
2. Exclusion criteria:

age under 18 years, elderly patients(>65 yrs), pregnancy, breast feeding, patient with bowel obstruction, and other structural intestinal disorders, gut hypomotility(chronic constipation(< 2 bowel movement/week for 1yr), hypomotility syndrome, megacolon, idiopathic pseudoobstruction), renal failure, congestive heart failure, liver failure, pre-existing electrolyte disturbance(hypercalcemia, hyperphosphatemia); refusal of consent to participate in the study.

Sampling design: Consecutive recruitment of consenting patients

Variables Predictor: split dose of PEG and sodium phosphate Primary Outcome: Quality of bowel preparation (Ottawa scale) Secondary Outcome: Tolerability (preparation completion, side effect) Confounding variables: age, gender, BMI, experience of colonoscopy, surgical history, bowel movement, comorbidity, indication, presence of GI symptoms, medication

Statistical issues

Hypothesis: Split dose bowel preparation with PEG will provide a better quality preparation and similar tolerability than that with sodium phosphate for morning colonoscopy.

Sample size.: Improving rate 20% in bowel cleansing efficacy(Ottawa scale), study power 80%, alpha-error(level of significance, P-value) 5%, mean value scale=5, effect size 1, SD=2.5-> sample size= 100/100

Inclusion Criteria:

• Adult outpatients(at least 18 years of age, under 65 years) who undergo scheduled colonoscopy for screening, cancer surveillance or want procedure with/without non-specific gastrointestinal symptoms

Exclusion Criteria:

• age under 18 years, elderly patients(>,=65 yrs), pregnancy, breast feeding, patient with bowel obstruction, and other structural intestinal disorders, gut hypomotility(chronic constipation(< 2 bowel movement/week for 1yr), hypomotility syndrome, megacolon, idiopathic pseudoobstruction), renal failure, congestive heart failure, liver failure, pre-existing electrolyte disturbance(hypercalcemia, hyperphosphatemia); refusal of consent to participate in the study.