1. The effects of an indigestible soluble polysaccharide (carboxy methyl cellulose: CMC) on broiler performance (body weight gain, food and water intake) and on chyme characteristics (moisture content, viscosity, pH, osmolality and retention time) in broilers were studied. 2. In semi-synthetic diets 0, 5.0 and 10.0 g/kg of cellulose was replaced by CMC on weight basis. These diets were fed to male broilers from 3 to 5 weeks of age. 3. When 10.0 g/kg CMC was included in the diet, food intake and body weight gain were reduced, compared to the 0, and 5.0 g/kg CMC diets. Food:gain ratio and water intake were increased at each CMC concentration. The significant quadratic response showed an increased response per 5.0 g/kg dietary CMC at the higher CMC concentration. 4. The viscosity in the supernatant of the chyme was linearly increased in all intestinal segments by CMC. A quadratic increase was observed in the crop. In the lower ileum, differences between the 5.0 and 10.0 g/kg CMC diets were not significant. 5. CMC increased the mean retention time of chromium in the duodenum and in the upper jejunum, and reduced the maximal rate of marker excretion. The transit time (first appearance of the marker in the excreta), however, was significantly reduced at the highest CMC concentration. 6. The osmolality of the intestinal fluid decreased less as the chyme moved from the duodenum into the lower ileum, with increasing concentrations of CMC. 7. The ileal pH was reduced linearly by the CMC content of the diet. 8. Based on a higher moisture content of the chyme in the CMC-fed birds, and the higher jejunal and ileal osmolarities in those birds, it was concluded that the efficiency of both digestion and absorption was reduced by CMC inclusion in broiler diets.