Among the twenty-three compounds isolated from bracken, kaempferol showed noticeable mutagenicity to Salmonella typhimurium, strains TA 100 and TA 98, with S-9 mix. With pretreatment of 'hesperidinase' the mutagenic activity of the boiling water extract was concentrated to the fraction containing astragalin. Several extracts and fractions were prepared for test of mutagenicity and the presence of other mutagens in bracken besides flavonoids was evidenced.