Since Teucrium chamaedrys and Teucrium montanum are the most popular plants used in the treatment of many diseases, we evaluated genotoxic potential of their methanolic extracts on cultured human peripheral blood lymphocytes (PBLs) using cytokinesis-block micronucleus (MN) assay. Cultures were treated with four concentrations of both plants (125, 250, 500 and 1,000 lg/ml), both separately and in combination with mitomycin C (MMC). The results revealed that extract of T. chamaedrys administered at the tested concentrations did not significantly affect the mean MN frequency in comparison to untreated cells. Methanolic extract of T. montanum increased the mean MN frequency in PBL at the tested concentrations, but significantly only at the concentration of 1,000 lg/ml. In all tested concentrations, the extract of T. chamaedrys significantly reduced the MMC-induced MN frequency, in a dose dependent manner (r = -0.687, p \ 0.01). The extract of T. montanum decreased the MMC-induced MN frequency at the tested concentrations, but statistically only at 125 lg/ ml. Both extracts administered alone did not significantly affect the nuclear division index (NDI) at the tested concentrations. In the combined treatments with MMC, the extract obtained from T. chamaedrys in the concentrations of 500 and 1,000 lg/ml significantly decreased NDI values in comparison to MMC-treated cells alone, while the extract of T. montanum significantly decreased NDI at all tested concentrations. Both extracts nonsignificantly decreased NDI at all tested concentrations in comparison to untreated cells. Our results suggest the important function of T. chamaedrys extract in cancer therapy, this methanolic extract may prevent genotoxic effects of chemotherapy in PBLs.