1. The effects of the addition of a non-ionic, anionic or cationic detergent to a diet containing 10% added fat on the digestibility of the protein, fat and carbohydrate have been studied.2. The non-ionic detergent aided the digestion of fat, but protein and carbohydrate digestibility were unaffected.3. An anionic detergent slightly, and a cationic detergent seriously, impaired the absorption of fat, and the cationic detergent also had an adverse effect on carbohydrate digestion. Neither affected protein digestion.