Antimutagens from Cirsium maritimum Makino (Compositae), purified chromatographically, were monitored for antimutagenic activity against Trp-P-2 in Salmonella typhimurium TA 98. Purification resulted in the isolation of a strong antimutagen, 5,49-dihydroxy-6,7dimethoxyflavone (cirsimaritin), and the 49-O-glucoside of cirsimaritin, cirsimarin, from the methanol extract. In addition, cirsimaritin was demonstrated to be a desmutagen that either acted directly on Trp-P-2 or inhibited metabolic activation.