A composition comprising, per litre of aqueous solution, from 30 to 350 g polyethylene glycol, from 3 to 20 g of an ascorbic acid component selected form the group consisting of ascorbic acid, a salt of ascorbic acid, or a mixture thereof, an alkali metal or alkaline earth metal sulphate, preferably from 1 to 15 g thereof, and optionally one or more electrolytes selected from sodium chloride, potassium chloride, and sodium hydrogen carbonate, and preferably also comprising flavourings, is effective in cleansing the gut in preparation for a endoscopy, especially colonoscopy. It is safer than conventional sodium phosphate-based gut cleansing compositions, and hence can be used for patients who would be at risk with sodium phosphate-based compositions, and is better tolerated than conventional PEG-based compositions, leading to better patient compliance and enabling effective out-patient use.