Antiviral activity against HSV-1 was shown by 11 extracts at non-cytotoxic concentrations. The IC 50 values (the concentration that protects 50% of the cells against destruction by viruses) ranged from <6.25 to 82 mg ml À1 . The highest activity against HSV-1 with IC 50 values <6.25 mg ml À1 was observed for the extracts of A. rivularis, B ciliata, Cassiope fastigiata and T. linearis. Moderate activity was shown by Cotoneaster integrifolius (IC 50 18 mg ml À1 ) and Clinopodium umbrosum (IC 50 19 mg ml À1 ). Weak activity (IC 50 50-82 mg ml À1 ) was found in the extracts of Bistorta affinis, Juniperus squamata, Oxytropis williamsii, Rhododendron anthopogon and Rubus foliolosus.