The effect on oro-caecal transit time of addition of soluble (guar gum) and insoluble (wheat bran) fibre to diets fed to seven healthy dogs at levels that have been shown to reduce post-prandial hyperglycaemia was assessed. Oro-caecal transit time was measured by sequential analysis of exhaled breath hydrogen levels. Median oro-caecal transit times were 105 min (range: 45 to 135), 113 min (range: 53 to 203) and 105 min (range: 75 to 195) after administration of a 770 g standard meal of canned food alone, or with the addition of 7.7 g wheat bran or guar gum, respectively. There was no significant difference between the oro-caecal transit times (p = 0.964) for the different diets when the results for all the dogs were pooled. The difference between diets was statistically significant for both maximal post-prandial hyperglycaemia (p = 0.035) and area of post-prandial hyperglycaemia under the post-prandial glucose curve (p = 0.006).