Antiviral activity was determined by dye uptake assay using neutral red as described by Mothana et al. (7) . Non-cytotoxic extracts were tested in concentrations of 100, 50, 25, 12.5 and 6.25 mg ml À1 . The antiviral tests of cytotoxic extracts started with the half of the individual CC 50 . The extracts were diluted 1 : 2 by medium. Confluent monolayers of Vero and MDCK cells were treated with 100 ml of extracts in four replicates for 30 min. After that Vero cells were infected with 30 TCID 50 of HSV-1 and MDCK cells with 30 TCID 50 of influenza virus A and incubated for 72 h at 37 C. TCID 50 (tissue culture infectious dose) is the virus dose that leads to the infection of 50% of the cells. The virus suspension and dilution medium without samples were added, respectively, to the cell cultures to serve as the virus control and cell control. The supernatant was replaced by 200 ml neutral red solution (0.005%) and the cells were incubated for 3 h at 37 C. After removal of the supernatant, the dye incorporated by viable cells was eluted with 100 ml ethanol/water/glacial acetic acid solution (50 : 50 : 1) by shaking for 15 min. The absorbance was measured at 540 nm and the percentage protection was calculated by the following formula (13):