Colonoscopy has become a widely-accepted procedure in the diagnosis and manage-ment of colonic disorders, mostly because of refined technique as well as improved equipements. For the colonoscopic examination of sufficient quality, adequate preparation is mandatory. Colonoscopy preparation should be theoretically rapid, effective, well-tolerable and safe, but the conventional method is not always satisfactory in this context. Recently-developed balanced electrolyte solution, containing polyethylene glycol and sodium sulfate, is associated with minimal absorption and secretion of water and electrolyte in the intestinal tract, when taken orally. In seventy patients who underwent total colonoscopy, we performed whole-gut lavage using this solution for the preparation, and prospectively evaluated its rapidity, effectiveness, patients' tolerance and safety. Preparation was accomplished within four hours in the majority of the patients on the same day of the examination, and was good to excellent in quality. The lavage method was preferred by the patients to the conventional method. No adverse effect was noted. We conclude the whole-gut lavage with nonabsorbable, nonsecretory balanced electro-lyte solution is a valuable method in preparation for colonoscopy.