Physico-chemical properties and the digestibility of carbohydrates (starch, b-glucan and arabinoxylan (AX)) were studied in the gastrointestinal contents of pigs fed diets based on oat bran. One diet was made of commercially prepared oat bran and another of oat bran milled to pass a 1 mm screen. The pigs were slaughtered and samples were collected quantitatively from 10 sites of the gastrointestinal tract either 1 or 3 h after the morning feeding. The viscosity of the liquid phase (obtained by centrifugation) of the stomach and small intestinal contents varied greatly between animals, and was not signiΓcantly di β erent between segments of the upper gastrointestinal tract. The molecular weight of b-glucan was reduced up to 20-fold in the upper gastrointestinal tract but was of a relatively low digestibility until the terminal ileum. The solubility (the fraction of the total content in the liquid phase of digesta after centrifugation) of b-glucan varied from 0Γ25 to 0Γ58 in the stomach and small intestine, whereas the solubility of AX was in the range of 0Γ04Γ0Γ16. Microscopic examination of digesta showed that b-glucan was retained in intact endospermic cell wall structures, which remained evident until the distal small intestine but was completely disrupted in the caecum. In spite of a cumulative digestibility of non-starch polysaccharides and AX of D0Γ90 in the large intestine, identiΓable fragments of aleurone cell walls resistant to complete microbial degradation remained.