Two test meals were taken in random order on separate days by 8 non-insulin-requiring diabetic volunteers after 14-hour overnight fasts. Addition of 16 g guar and 10 g pectin to the control meal containing 106 g carbohydrate decreased markedly and significantly the rise in blood-glucose between 30 and 90 minutes and also resulted in significantly lower insulin levels between 30 and 120 minutes. When these meals were fed to 3 insulin-dependent diabetic subjects, a similar flattening of the post-prandial glucose rise ensued. This addition of certain forms of dietary fibre to the diet of diabetics significantly decreases post-prandial hyperglycaemia and would be expected to improve the control of blood-glucose concentration.