Abstract AIM: Poor mucosal coating, due to excess of fluid in the colon lumen, is a problem when the oral lavage method (4 litres of an iso-osmotic saline solution containing polyethylene glycol) is used as a preparation for double-contrast barium enema. Our aim was to assess the value of prior administration of sennosides to obtain a clean colon with a reduced volume of polyethylene glycol (PEG)-saline solution, but maintaining good mucosal coating. MATERIALS AND METHODS: after a 2-day low-residue diet, three different oral preparations, were compared: (i) 4litres of a PEG-saline solution (SELG®) and 15 mg of bisacodyl (116 patients, SELG-4 group); (ii) 156 mg of sennosides, 15 g of magnesium sulphate, and 2 litres of water (116 patients, SennMg group); (iii) 156 mg of sennosides and 2 litres of SELG (116 patients, SennSELG group). Compliance, complaints, cleansing, mucosal coating, and fluid retention were evaluated. RESULTS: Compliance, complaints, cleansing, mucosal coating, and fluid retention of mild nausea was observed in SELG-4 group, of mild abdominal cramping in SennMg group, of substantial abdominal cramping in SennSELG group ( P < 0.02). Cleansing was better in SennSELG than in both the SELG-4 ( P = 0.0003) and SennMg ( P = 0.0353) group. Mucosal coating was better in SennMg than both SELG-4 ( P = 0.0034) and SennSELG ( P < 0.0001) group. There was more residual fluid in the SennSELG group than both in SELG-4 ( P = 0.0029) and SennMg ( P = 0.0059) group. CONCLUSION: For colon cleansing, the combination of sennosides and PEG-saline solution was better than either the 4 litre PEG protocol or the combination of sennosides and magnesium sulphate. For mucosal coating, the protocol combining sennosides and magnesium sulphate was more effective than either protocols using the PEG-saline solution. This may be due to the interaction of residual magnesium ions in the colon lumen with the barium suspension.