Although some dietary fibres (DF) improve glucose tolerance by slowing carbohydrate absorption, other mechanisms are certainly involved. Some of the entero-hormonal responses after DF were investigated in six patients with impaired glucose tolerance and reactive hypoglycaemia. All patients received two different breakfasts, each containing 25 g of starch supplied either as white bread (WB) or a fibre-enriched bread preparation (FB): 4 g hemicellulose and 4 g guar. Metabolic and hormonal responses were evaluated over 5 hours. Compared to WB, the FB had a blunting effect on the resulting blood glucose peak (116 +/- 9 mg/100 ml with FB vs. 148 +/- 15 with WB P less than 0.025) or trough (88 +/- 3 mg/100 ml with FB vs. 79 +/- 5 with WB), and upon the insulin response at 60 min (20 +/- 4 micro U/ml with FB vs. 70 +/- 20 with WB). Gut glucagon immunoreactivity was diminished with FB at 90 min (185 +/- 39 vs. 242 +/- 42 P less than 0.05) and 150 min (180 +/- 39 vs. 242 +/- 40). Pancreatic glucagon was initially similar after FB and WB, but a significant rise was observed with FB at 180 min (116 +/- 17 pg/ml vs. 67 +/- 18 P less than 0.05). The improvement of the blood glucose pattern with DF, especially the suppression of reactive hypoglycaemia, seems to depend partly on reduced and delayed response of the entero-hormonal axis. This in turn results in a better synergistic secretion of insulin and glucagon in the late post-prandial period.