Extracts of Viscum album from different host trees (Iscador®Qu, M, P and A) and isolated mistletoe lectin showed distinct gene-expression profiles using cDNA microarrays. We were able to confirm that genes of apoptosis, the cell cycle and the immune system were affected by mistletoe preparations and we also found that signal transduction, cell communication and cancer related pathways were overregulated in the tested breast cancer (HCC-1937, MCF-7, KPL-1, Mfm-223) and lymphoma cell lines (WSZ-NHL). The effect of a specific mistletoe extract on a particular cell line was individual, so that the distinction between the reaction of the cell type and/or the influence of the mistletoe preparation could be used in targeted mistletoe therapy