This thesis deals with selected herbal ingredients and their importance with regard to tumor treatment. In the first section of this work the definition, the differentiation as well as the molecular biologic basis of a tumor disease are worked out. In addition, statistics are intended to illustrate the chronological development, the number of new cases and the mortality rates of cancer in different countries. Then, the classical treatment options for cancer as well as the gene activity of a tumor cell are discussed. In addition to the general definition of phytotherapeutics, a further section focuses on the herbal active ingredients and their usefulness for cancer treatment, with a focus on the active substance taxol. In addition to the botanical features of Taxus brevifolia from which taxol is derived, a brief historical outline, as well as findings on the active ingredient in vitro and in vivo will highlight the importance of this substance. In order to underline its efficacy in breast cancer and ovarian carcinoma, selected studies are cited. Furthermore mistletoe as a supplementary active substance in cancer treatment is to be mentioned in this thesis. A final chapter, which deals with some selected plants and their contents, is intended to illustrate their significance, both now and in the future.