Equisetum myriochaetum is a Mexican plant used in folk medicine to treat kidney diseases and type 2 diabetes mellitus. The main constituents of the phytoextract are flavonol glycosides (kaempferol), phytoesterols and carbohydrates. In this study, phytotherapeutic extracts from Equisetum myriochaetum were investigated for genotoxicity in the in vivo wing spot test in Drosophila melanogaster and in the in vitro human micronucleus test. No acute toxicity of the phytoextract could be determined in Drosophila or in human lymphocytes in culture, ranging from 0.78 microg/ml to 3700 microg/ml for the wing assay and between 12.5 microg/ml and 500 microg/ml for the micronucleus test. The Drosophila wing somatic mutation and recombination test (SMART) was applied in the standard version with basal biotransformation activity as well as in a variant version with increased cytochrome P450-dependent bioactivation capacity. The ranges of exposure concentrations for these genotoxicity experiments were between 0.78 microg/ml and 500 microg/ml. The human micronucleus test in vitro was performed with cultured lymphocytes obtained from four healthy donors. The concentrations assayed for these experiments ranged from 12.5 microg/ml to 500 microg/ml. No statistically significant increase was observed between treated series when compared with a concurrent negative (water solvent) control series in either assay. The results demonstrate clearly that the phytotherapeutic extract from Equisetum myriochaetum, under the experimental conditions tested, is not genotoxic in the in vivo experiments or in the in vitro studies.