Abstract: Compositions of therapeutic or dietetic use have been prepared comprising vegetable fibre and lactulose. The two components have demonstrated a strong reciprocal synergic effect, by which with compositions which provide a daily quantity of 0.5-2.5 g of raw fibre and 5-10 g of lactulose it is possible to obtain therapeutic effects on the gastrointestinal system which are better than those obtainable by a daily administration of 10-20 g of raw fibre or 10-20 g of lactulose.