Application of Viscum album L., the white berry mistletoe, is one of the most widely used unconventional remedies in Europe to treat hypertension and arteriosclerosis, arthrosis and/or arthritis, and, even more important, cancer. Studies in cancer patients have shown significant increases of immunological parameters. Some 50 clinical studies, including historical, retrospective, prospective and randomized trials, reported extended survival times, improved quality of life, or tumour regression with mistletoe therapy. Although the quality of the trials is in most cases poor, several studies suggested a positive effect (for review see Kiene, 1989, 1996; Kleijnen and Knipschild, 1994). However, the majority of these studies do not fit the current standards of research. Gabius and co-writers (1994) stated an obvious discrepancy between the popularity of mistletoe extracts and their classification as a non-conventional treatment modality with unproven efficacy in oncology.