Background: A prospective randomized trial to assess the cleansing ability and tolerance of bowel preparations for colonoscopy was conducted in a group of 953 patients. Methods: The bowel cleansing methods were: sennoside calcium, polyethylene glycol (PEG) lavage, oral sodium phosphate (NaP) in one 90-ml dose, oral NaP in 2 doses (90 ml + 45 ml), oral NaP in 2 doses (45 ml + 90 ml), oral NaP in 2 doses (45 ml + 90 ml) plus cisapride, and oral NaP in 2 doses (45 ml + 90 ml) plus domperidone. Results: The cisapride-containing procedure was abandoned partially through the study because of its adverse effects. The colon cleansing ability in groups with NaP plus cisapride and NaP plus domperidone was significantly better than the other groups (p<0.05). Tolerance to sennoside calcium and PEG lavage in comparison to the other groups was significantly worse (p<0.05). Conclusion: Two doses of NaP solution (45 ml + 90 ml) plus domperidone for colon cleansing is a safe, effective, rapid, inexpensive and well tolerated.