Antiviral activity against influenza virus A was shown by 20 extracts at non-cytotoxic concentrations. The IC 50 values ranged from <6.25 to 97 mg ml À1 . The highest activity was shown by the extracts of A. filicinus, A. rivularis and Verbascum thapsus with IC 50 < 6.25 mg ml À1 . In addition, the extracts of Allium oreoprasum, A. strigilosa and B. ciliata also exhibited high activity (IC 50 values from 8 to 10 mg ml À1 ). Moderate activity (IC 50 values from 17 to 50 mg ml À1 ) was demonstrated by 11 extracts. Weak activity (IC 50 values from 78 to 97 mg ml À1 ) was shown by three extracts ( Table 2 ). The extracts of A. rivularis and B. ciliata were found to be highly active against both viruses.