Infection of Vero cells with herpes simplex virus type-1 (HSV-1) resulted in a series of changes in intra-cellular free calcium concentration $([Ca^{2+}]_i)$. A significant and maximal decrease $[Ca^{2+}]_i$ was observed at 4 hours postinfection (hr p.i.) in HSV-1-infected in Vero cells. Inactivation of HSV-1 with UV irradiation and heat treatment abolished HSV-1-induced decrease in $[Ca^{2+}]_i$ at 4 hr p.i. in Vero cells. And the degree of the decrease in $[Ca^{2+}]_i$ was dependent on the amount of input virus. Taxol, which stabilizes the polymerization of microtubule blocked HSV-1-induced decrease in $[Ca^{2+}]_i$ at 4 hr p.i., suggesting that microtubule may mediate the transport of HSV-1 nucleocapsid to the nucleus of infected cell. Treatment of HSV-1-infected Vero cells with metabolic inhibitors such as cycloheximide, cordycepin, or acyclovir partially reversed the decrease in $[Ca^{2+}]_i$ at 4 hr p.i.. Thus, it is suggested that HSV-1 induced decrease in $[Ca^{2+}]_i$ at 4 hr p.i. in Vero cells may play an important role in the multiplication of HSV-1.