The objective of the present study was to evaluate the effects of dietary inulin and sucrose on the fermentation profile of the gastrointestinal microflora in chicken. Day-old broilers (n = 80) were assigned to four dietary treatments, either fed a basal diet or the same diet supplemented with sucrose (4%), inulin (1%) or sucrose and inulin. At day 35, birds were killed and pH, lactate, ammonia, short chain fatty acids (SCFA) and biogenic amines were determined in different parts of the digestive tract. Final body weights and the relative weights of liver, pancreas, crop, gizzard and small intestine were not influenced by treatment. The relative weights of the empty caeca and of the caecal digesta were higher with the diets containing inulin while caecal pH and ammonia were reduced. Lactate concentration was reduced in the crop (p < or = 0.01) and gizzard (p < or = 0.001) of sucrose-fed groups, while it was increased (p < or = 0.01) in the jejunum of inulin-fed group. Ammonia in the crop (p = 0.089) and gizzard (p = 0.067) tended to be lower in the group receiving inulin plus sucrose. Amongst SCFA, only acetate was detected in the crop and gizzard contents that tended to be lower (p = 0.09) in the crop digesta of sucrose plus inulin-fed group. N-butyrate (mol %) was higher (p < or = 0.001) in the caecal digesta of inulin-supplemented groups without affecting total SCFA. Dietary inulin elevated the concentration of putrescine in the jejunal and caecal contents. In the caecal digesta, total biogenic amines were increased (p < or = 0.001) in sucrose plus inulin-fed group without affecting production of biogenic amines in the jejunum. In conclusion, inulin could reduce the pH in the lower gastrointestinal tract of broilers, while sucrose had no acidifying influence in the upper digestive tract. Inulin enhanced the concentration or metabolic activity of butyrate-producing bacteria in the caecum. Further studies are needed to investigate the potential effect of inulin on the intestinal microbial composition.