During herpes simplex virus type 1 (HSV-1) lifelong latency in human peripheral sensory ganglia (PSG), only the viral latency-associated transcript (LAT) gene is expressed. This raises the possibility that this gene is involved in establishment of latency of the virus, its maintenance, or reactivation. Here we present data that indicate yet another independent function of the LAT gene: interference with HSV-1 superinfection of latently infected neurons. Neuronal cells stably expressing the LATs are protected from infection with HSV-1, but not from infection by other RNA and DNA viruses, including HSV-2. These unexpected findings may explain the observation that human PSG are latently infected with just a single strain of HSV-1, despite repeated exposure during life to multiple viral strains. Thus, the LATs may protect the latent HSV-1 reservoir from cytopathic superinfections, and at the same time the host is protected at the viral entry site from HSV-1 insults that may eventually cause viral encephalitis.