An aqueous mistletoe extract (AME, the active principle of Lektinol) was investigated for its genotoxic potential in a wide range of in vitro studies, according to the actual international standard guidelines. Gene mutation tests on bacteria and mammalian cells in vitro all gave negative results. From the findings of cytogenetic studies, there was no indication of a clastogenic activity in human lymphocytes. A cell transformation assay revealed no malignant changes of Syrian hamster embryo cell cultures. In summary, the results suggest that AME has no genotoxic potential in vitro.