Summary1. The influence of 14 carbohydrates on gastrointestinal absorption of radiostrontium and radiocalcium was studied in the rat. 2. Cellobiose, sorbose, ribose, xylose, lactose, raffinose, melibiose, glucosamine, mannitol and sorbitol significantly enhanced alkaline earth absorption whereas glucose, galactose, fructose and sucrose had little or no effect. 3. In a balance-type study with Sr85, enhanced retention due to dietary lactose as compared with dietary sucrose could be accounted for by increased intestinal absorption rather than by direct effect on skeletal ossification. 4. Effectiveness in ability to enhance calcium and strontium absorption appeared to be positively correlated with a prolonged residence time of the carbohydrate in the gut or absorption of carbohydrate by a passive mechanism.