The experiment was conducted to proof the new natural plant extracts (Fagopyrum Mill. (buckwheat), Crataegus ex L., (hawthorn), Hypericum L. (St -John's -wort's) and Helichrysum arenarium) and selected flavonoids as reference substances for the in vitro. The probing was performed as considering four different parameters: the antioxidant activity, the antiradical activity – DPPH test, the DPH te...