- The antiviral activity of plant ethanol extracts against Herpes Simplex Virus-1 and -2 (HSV-1 and HSV-2) and Varicella-Zoster Virus (VZV) was investigated in vitro . Ficus binjamina , resistant to plant viruses, and Lilium candidum, which has a high susceptibility to plant viruses were used. Leaf extracts of F. binjamina inhibited all studied viruses, while its fruit extracts inhibited only VZV. L. candidum leaf extracts had no effect on VZV but strongly inhibited HSV-1 and slightly HSV-2. None of the extracts showed significant cytotoxic effect on uninfected Vero cells even at a concentration of 250 μg/ml (CC 50 > 400 μg/ml). The greatest antiviral effect was obtained when extracts were added to cells at the time of infection, whereas a partial inhibitory effect was observed when they were added post-infection. There was indirect evidence for strong interactions between the plant extracts and the viruses and weak interactions with the cell surface.