Saponins are plant glycosides with favorable anti-tumorigenic properties. Several saponins inhibit tumor cell growth by cell cycle arrest and apoptosis with IC50 values of up to 0.2 microM. We discuss diverse groups of saponins (dioscins, saikosaponins, julibrosides, soy saponins, ginseng saponins and avicins) investigated in relation to tumor therapy and focus on cellular and systemic mechanisms of tumor cell growth inhibition both in vitro and in vivo. The review also describes saponins in combination with conventional tumor treatment strategies, which result in improved therapeutic success. Some combinations of saponins and anti-tumorigenic drugs induce synergistic effects with potentiated growth inhibition.