To evaluate the effects of a fibre-rich diet on blood glucose and serum lipoproteins, eight diabetic patients, four on insulin and four on oral hypoglycaemic drugs, were put on three different diets, a different one for each consecutive 10-day period: diet A (carbohydrate 53%, fibre 16 g), diet B (carbohydrate 53%, fibre 54 g), and diet C (carbohydrate 42%, fibre 20 g). All diets had identical polyunsaturated/saturated fat ratios. Both 2 h post-prandial glucose and mean daily glucose levels were significantly lower after diet B than after either of the two other diets, as were total and LDL cholesterol levels. Total and VLDL triglyceride levels after diet B were significantly lower than those after diet A but almost identical to those after diet C. HDL cholesterol concentration was not affected by dietary fibre but was significantly increased by the low-carbohydrate diet. A high-fibre, normal-carbohydrate diet (the fibre coming exclusively from foodstuffs with a naturally high content of fibre) improves blood glucose control and decreases the concentration of atherogenic lipoproteins in diabetic patients. This effect is independent of the amount of available carbohydrates in the diet.