Perfusion of the gut lumen with 2 ml of isotonic solutions showed uniform absorption of glucose and water over the four 15-minutes study periods, the absorption being maximum in jejunum and least in colon. With hypertonic solutions the glucose absorption decrease was related to the increasing osmolarity and duration of exposure to the solution as well as the nature of the substance used. Histological changes reflecting impaired functions were localised to the tips of the villi and were observed on exposure to hypertonic solution for 45 minutes or more.