Measurements were made of the absorption up to the end of the ileum and of the urinary excretion of D-xylose, L-arabinose and D-galacturonic acid given to pigs. When given at a rate of 4g/day mean ileal digestibilities were 0.96 for xylose and 0.76 for both arabinose and galacturonic acid. Mean urinary excretion, as a proportion of the daily dose, was 0.35 for xylose, 0.42 for arabinose and 0.01 for galacturonic acid. When arabinose and galacturonic acid were given at a rate of 30 g/day mean ileal digestibilities were 0.56 and 0.34 respectively; the corresponding proportions of the dose excreted in the urine were 0.42 and 0.02. Indirect calorimetry was used to measure the heat increment associated with a single large dose of each carbohydrate. The mean proportion of the energy of these supplements which was retained amounted to 0.75 for xylose, 1.00 for arabinose and 0.75 for galacturonic acid.