The possibility of modulating postprandial metabolic responses in diabetics by an increase in the amount of soluble fibre rather than by the use of the high amounts of total dietary fibre (DF), so far strongly advocated, was investigated. Soluble and insoluble DF components of common foodstuffs were analysed and the data utilized to formulate three different meals with similar quantities of available carbohydrate, protein and fat and differing only in the quantity and quality of DF: low fibre (LF), high soluble fibre (HSF) and high insoluble fibre (HIF). Ten NIDDM patients in good metabolic control received each test meal in randomized order at 2-week intervals. The postprandial blood glucose and serum insulin responses to the LF and HIF test meals were similar. The HSF meal produced significantly lower glucose (P less than 0.001) and insulin (P less than 0.05) responses, compared to either LF or HIF meals. Such results may be of relevance in the formulation of diabetic diets in order to prevent an excess of insoluble fibre, so improving patients' compliance. Fruits and vegetables may be used advantageously to increase quantities of soluble fibre, limiting excesses of legumes or guar additives.