The infection of baby hamster kidney (BHK21) cells by the Indiana strain of vesicular stomatitis virus (VSV) causes a rapid loss of the ability of the cells to be superinfected by VSV virions or defective-interfering particles. This exclusion phenomenon is at the level of virus penetration and requires viral gene expression and a functional VSV transmembrane glycoprotein G. Infection with the New Jersey serotype of VSV also inhibits the uptake of the Indiana serotype. However, infection of BHK21 cells with either encephalomyocarditis, Newcastle disease, or influenza A viruses does not inhibit superinfection by VSV.