Background and Aim : Viral infections, particularly infections caused by herpes simplex virus (HSV) are considered as one of the most important worldwide public health concerns, due to their devastating impacts on human body. In recent years, along with the increased drug-resistant strains in virus of all types and the side effects of chemical drugs , natural remedies having fewer side effects have been of interest to researchers. Eremostachys labiosiformis (Popov) Knorring is type of flowering plant belonged to Lamiaceae family. It has been identified as the desert hyacinths. This plant contains medicinal active compounds including alkaloids, saponins, flavonoids and tannins. In vitro experimental systems showed that these compounds have Antiinflammatory, anti-allergy, anti-viral and anti-tumor properties. The aim of this study was to evaluate the antiviral effects of E.labiosiformis extract on herpes simplex virus type 1. Researche which done on the health benefits of this plant is the first research that will be carried out in this area in the world. Methods : The methanol extract of the aerial parts of E.labiosiformis was prepared by 80% methanol maceration and Vero cells were cultured in medium containing 10% fetal bovine serum in 96- well micro plates. Cytotoxic effects of different concentrations extract on Vero cells were examined using MTT Method (3- (4, 5- dimethylthiazol-2-yl)-2, 5 diphenyl tetrazolium bromide) .TCID50 method was applied to determine the viral titer (50% Tissue Culture Infection Dose). The inhibitory effects of the extract on herpes simplex virus type 1 within two phases including extracellular (Pre-incubation of cell monolayer with E.labiosiformis extract before virus infection), direct contact (Incubation of HSV-1 virus with E.labiosiformis extract before infection) and Intercellular (Incubation of Vero cell monolayer with E.labiosiformis extract cells after HSV-1 virus infection) were evaluated by CPE (Cytopathic Effect) and MTT Method
