1. Whole body glucose turnover and absorption of a 50 g glucose drink was studied in six healthy volunteers on two occasions, 4 h after a ‘breakfast’ of 50 g of glucose, mixed on one occasion with 20 g of guar gum. 2. Plasma glucose concentrations were significantly reduced with guar gum compared with those obtained without guar gum (P < 0.0001). 3. Whole body glucose turnover studied by an intravenous primed dose constant infusion technique using d-[3-3H]glucose showed no significant difference between the two groups: 353 ± 15 mmol with guar and 350 ± 9 mmol without guar. 4. Total oral glucose absorption, followed with a D-[1-14C]glucose tracer, was significantly decreased by guar treatment, being 219 ± 3 mmol with guar and 239 ± 5 mmol without guar (P < 0.05). 5. Serum insulin levels were lowered by guar treatment (P<0.05) while those of C-peptide, gastric inhibitory polypeptide, glucagon, Cortisol and pancreatic polypeptide did not differ significantly. 6. Blood lactate concentrations were raised in the guar treated group (P < 0.05) whereas pyruvate, alanine, glycerol and 3-hydroxybutyrate concentrations did not differ significantly. 7. These results support the suggestion that guar improves second-meal tolerance to glucose by decreasing absorption.