The influence of guar gum on gastric emptying of liquids in healthy volunteers and on mouth-to-caecum transit time in controls and partially gastrectomized patients has been studied. Together with a flattening effect on blood glucose profiles after a liquid glucose load, guar significantly delays mouth-to-caecum transit time both in healthy controls and partially gastrectomized patients. The retardation of transit is not explicable by a delay in gastric emptying, as can be shown by means of an isotope technique. Only in "quick starters' was a delay in initial gastric emptying observed. The exponential phase of gastric emptying remained unaffected. Moreover, it is shown that the prolongation of mouth-to-caecum transit time is not mediated by factors operating at the level of the pyloricantral region. Delayed small-bowel passage by guar might modulate absorption of glucose by increasing the unstirred layer resistance and, in the non-steady state, by limiting the absorptive area initially covered by a bolus.