The antimutagenic activity of Angelica archangelica L. aqueous and alcohol extracts of thio-TEPA against mutagenicity was examined by the micronucleus test in murine bone marrow cells. The reduction of Thio-TEPA's mutagenic activity was more profound when the extracts were injected 2 hours before thio-TEPA treatment, as seen during simultaneous treatment. The observed reduction of micronuclear frequencies was as high as 77%.