The influence of non-starch polysaccharides (NSP) in growing and adult pigs is discussed. It is evident that the pig, especially the adults, has a considerable propensity to degrade NSP that enter the large intestine that, in turn, can contribute a significant proportion of maintenance energy requirements. Soluble NSP fed to pigs may also have anti-nutritive effects during their passage through the small intestine but this may only be true for piglets but can be counteracted by in-feed enzymes. Non-nutritional effect of NSP includes modification of sow behaviour and odour emission. Evidence has been presented to implicate the presence of fermentable sources of carbohydrate, i.e., soluble NSP and resistant starch, in the clinical expression of swine dysentery. Although the exact mechanisms where these carbohydrates have such an effect have yet to be elucidated, it is suspected that changes in microbial populations and/or numbers in the large intestine are implicated. This provides a good example whereby disruption of the stable microflora by nutrition has an important influence on gut function and health in the pig.