The effects of dietary supplementation with granulated guar gum (21 g/day in three divided doses at the main meals), were compared with placebo response during three months in a double-blind, cross-over trial in 11 Type 2 (insulin-independent) diabetes. The nine patients who complete the study (two dropped out because of side-effects) showed a significant reduction in both basal and post-prandial hyperglycaemia as well as of urinary excretion of glucose during guar gum supplementation. No change in mean bodyweight was observed during the study. Mean fasting and post-prandial plasma insulin levels were similar during both study periods, but the two subjects who received no oral hypoglycaemic agents had lower insulin levels during the guar gum period. Mean serum total- and LDL-cholesterol concentrations were significantly lower during the guar gum period, whereas the HDL-cholesterol level remained unchanged. Long-term administration of guar gum induced a sustained improvement in diabetic control in Type 2 diabetes.