1. Dietary fibre, such as pectin, delays gastric emptying and may enhance post-prandial glucose tolerance. Agar, which is high in fibre content, is widely used in the traditional Japanese diet. Although long-term diet therapy with agar decreases fasting plasma glucose levels in diabetes, knowledge is lacking about the acute effects of agar on gastric emptying and the post-prandial glycaemic profiles. The present study was designed to investigate the acute effects of agar. 2. Ten healthy male volunteers were studied on three occasions with three different test meals (450 kcal/500 mL): (i) a fibre-free meal; (ii) a meal with 2.0 g agar; or (iii) a meal with 5.2 g pectin. On each occasion, participants underwent a [(13)C]-acetate breath test along with serial blood sampling. To quantify gastric emptying, the half [(13)CO(2)] excretion time (t((1/2)b)) and the time for maximal [(13)CO(2)] excretion rate (t(lag)) were determined. The post-prandial glycaemic response was expressed as an incremental change from the fasting value at each sampling time. Data were analysed using repeated-measures analysis of variance (anova), followed by a post hoc paired Student's t-test with Bonferroni adjustment. 3. The time-course for respiratory [(13)CO(2)] excretion differed significantly among the three test meals (P = 0.0004, anova). Compared with the control meal, [(13)CO(2)] excretion was significantly lower following consumption of the agar meal (between 40 and 105 min post-prandially; P < 0.025, Student's t-test) and the pectin meal (between 40 and 180 min post-prandially; P < 0.025, Student's t-test). Among the three meals, significant differences were found in t((1/2)b) (P = 0.002, anova) and t(lag) (P = 0.011, anova). Compared with the control meal, the agar and pectin meals exhibited a significantly prolonged t((1/2)b) (P = 0.007 and P < 0.0001, respectively, Student's t-test) and t(lag) (P = 0.006 and P = 0.002, respectively, Student's t-test). Neither the agar nor pectin meal affected the post-prandial glucose profile. 4. In healthy adults, agar and pectin delay gastric emptying but have no impact on the post-prandial glucose response.