Iso-Giuliani is a new improved-taste isoosmotic PEG-electrolyte solution for colon cleansing. In a randomized study, we have compared the effectiveness, tolerance and patient acceptance of 3 dosage volumes of this solution with a standard preparation in 191 patients undergoing colonoscopy. Iso-Giuliani 3 1, and 4 1 proved better colonic preparations as compared with the standard preparation (P less than 0.01). However Iso-Giuliani, 21 was sufficient for satisfactory cleansing, especially in the rectosigmoid. Patients in the standard preparation group experienced more cramps than did those in Iso-Giuliani groups. Patient acceptance was significantly better for Iso-Giuliani than for the standard preparation. The ingestion of Iso-Giuliani represents a safe, effective and well-accepted method of colon cleansing, and is our elective method of preparation for colonoscopy.