The results of our investigations indicate that dietary treatment with inulin or oligofructose incorporated in the basal diet for experimental animals: (i) reduced the incidence of mammary tumors induced in Sprague-Dawley rats by methylnitrosourea; (ii) inhibited the growth of transplantable malignant tumors in mice; and (iii) decreased the incidence of lung metastases of a malignant tumor implanted intramuscularily in mice. Moreover, besides such cancer risk reduction effects, the dietary treatment with inulin or oligofructose significantly potentiated the effects of subtherapeutic doses of six different cytotoxic drugs commonly utilized in human cancer treatment. If confirmed, such dietary treatment with inulin or oligofructose potentiating cancer therapy might become an interesting approach to complement classical protocols of human cancer treatment without any additional risk for the patients.