We report here the effect of treatment of purified protein from Trichoderma Rifai fungi on the expression of viral antigenes in the infected Vero cells. At the very low level, of infective virul multiplicity of cells the specific inhibitory effect was observed in the presence of as little protein as 0.7 ng/ml. At the higher concentrations of this protein agent (up to 70 ng/ml) the complete inhibition of viral cytopathic action was reached, while at its concentration of 7 μg/ml the cytotoxic effect did occur along with the inhibitory effect of ∼50%. This was assesed by immunoblot analysis with highly specific antiherpetic serum (dilution 1:50,000) and DNA synthesis assay. In addition, under the condition of high infective multiplicity (∼100 pfu/cell) about 1000 times protein-agent-induced reduction of HSV-1 did occur. Differential expression of viral antigens showed that Trichoderma Rifai protein blocks the synthesis of both viral envelope (gB and gD) and nucleocapside (p40 and p44) proteins. The results suggest that fungal protein supress the reproduction of HSV-1 and the synthesis of viral antigenes.