Note that by 30 days post-infection, however, the viability of the culture was quite low in comparison to earlier time points (Fig. 5A ). To further test the fate of the surviving endothelial cells, we examined viability of infected cells by staining with annexin V and PI (Fig. 5C ). MB114 cells were 92.4% (60.6 SEM) viable (annexin V negative, PI negative) at two days post-infection and 72.5% (614.5 SEM) viable at four days post-infection. At six days postinfection all MB114 cells were non-adherent and 31.0% (610.74 SEM) of these non-adherent cells were viable. In contrast to MB114 cells, dying cells dominated infected 3T12 cultures at six days post-infection These data indicate that many MB114 cells died early during infection, and in agreement with our proliferation data ( Fig. 5A and 5B ) the population of viable cells increased to 86.4% (60.6 SEM) of the culture by 12 days postinfection. However, by 30 days post-infection dying cells finally dominated the infected culture. These data support that the subset of cells surviving and proliferating at six days post-infection were unique their extended survival, but did not remain viable indefinitely. Of significance, during the course of this infection most of the cells expressed the lytic glycoprotein gp150 on their surface at both early and late time points (Fig. 2C and Fig. 3C) . Moreover, the percentage of cells expressing gp150 did not change markedly with time ( Fig. 2C and Fig. 3C ). These data indicate that the vast majority of viable, infected endothelial cells were undergoing active viral replication, and that these cells were neither latently infected nor had escaped infection.