Thirty-six male castrated pigs (German Landrace; body weight: 26-40 kg) received a diet consisting of (%): barley, 31; rye, 30; wheat bran, 18; soyabean meal, 15.5 and premixes 5.5, during a 3-week period. The diet contained 18.9% non-starch-polysaccharides (NSP) with 4.5% (β-glucan, 9.4%) arabinoxylan and 2.9% cellulose and was fed to another 18 pigs. This diet was supplemented with a commercially available enzyme premix (600 FXU xylanase and 56 FBG 1,4-β-glucanase per kg feed) and was fed to another 18 pigs. At the end of the feeding period the animals were killed at three different times after feeding (1, 3 and 6 h postprandial). pH, ammonia concentration and volatile fatty acids (VFA) were determined in the digesta of the stomach and of the small intestine, which was divided into two sections of equal length. The pH in the upper digestive tract was not significantly influenced by enzyme supplementation. The concentration of NH₃ in these sections was slightly lower compared with the unsupplemented control (P>0.05). Propionate was the most important volatile fatty acid in the stomach (44.7 molar percentage of VFA) and in the small intestine (76.6 and 75.3 molar percentage in the first and second section). It was found that the VFA concentration tended to be lower in the stomach (acetate: P<0.05) and higher in the small intestine (particularly propionate, P>0.05) if NSP degrading enzymes were added.