Freeze-dried ileal ef¯uent from cannulated pigs fed rye bread diets based on either whole rye or one of three rye milling fractions enriched in pericarp/testa, aleurone and endosperm was incubated in an in vitro fermentation system with faecal inocula from pigs fed a whole grain rye diet. Three and 48 hours of in vitro degradation of arabinoxylans were comparable to the caecal and faecal degradation respectively. The productions of short-chain fatty acids were highest from the ileum samples of the diets high in fermentable carbohydrates (whole rye, aleurone and endosperm). However, fermentation of the pericarp/testa ileum sample produced half the amount of short-chain fatty acids resulting from the other ileum samples despite the fact that the pericarp/testa carbohydrates (CHO) were not fermented at all. Treating the pericarp/testa with alkali prior to the incubation increased fermentability considerably (from 0 to 49% of total arabinoxylans) and suggested that, at least in ligni®ed tissue, alkali-labile cross-links were more important determinants of arabinoxylan (AX) degradability than AX structure itself. Oxidative deligni®cation of the pericarp/testa ileal ef¯uent increased fermentability too, but to a much lower degree, which indicates that the type and extent of links between polymers and lignin rather than the amount of lignin are important in determining degradability.