The regulatory role of neuro-immune pathways in various infectious disease states is an interesting area of investigation due to its important therapeutic potential. In this study the effect of substance P (SP) on nitric oxide (NO) production of HSV-infected macrophages and its relation with incubation time and also the cytopathic effect of virus in the presence of SP are considered. As we have observed, substance P enhances NO production both in HSV- and mock-infected macrophages and this effect has been diminished or disappeared after 24 h. It has also been observed that SP enhances the cytopathic effect of HSV in a time dependent manner with the most effect at 10 h after stimulation with SP. We have also observed that HSV-1 cytopathic effect has not been significantly affected by pretreatment of macrophages with SP (2, 10 or 24 h before HSV infection). It can be concluded that the neurotransmitter SP has a significant role in modulating macrophage function and thus innate immunity processes in healthy and HSV-infected cells.