Different sources of dietary fibre (defined here as non-starch polysaccharides, NSP) are hydrolysed to varying degrees in the GI tract of pigs. Unlike starch, NSP cannot be digested to its monomeric constituents by mammalian enzymes, but instead must be fermented by the gut microflora, to yeild volatile fatty acids (VFA). These VFA, like the glucose derived from the digestion of starch, are subsequently absorbed and metabolised to yeild ATP, but with a lower efficiency than glucose. Clearly, therefore, knowledge of the relative amounts of products of fermentation and digestion which are absorbed, will enable the nutritive value of a feed to be described more accurately. We report the time course of absorption of glucose, VFA, lactate, and α-amino N from semi-purified diets containing two contrasting sources of NSP, wheatstraw (WS) and sugar beet pulp (SBP), by growing pigs.