During this course of infection, the number of intact cells in the culture increased from 7.08610 5 (60.16 SEM) to 8.51610 6 (60.28 SEM) during the first six days of culture, a ten-fold increase. A corresponding increase in the percentage of membrane viable cells also occurred during this time. Subsequent to day 12 post-infection, the total number of intact cells began to decrease, as did the overall viability of the culture (Fig. 5A ). The observed increase in both intact cell number and percent viability during the first six days of culture, concurrent with positive gp150 staining ( Fig. 2C and Fig. 3C ), indicated that endothelial cells were intact and proliferating in culture while maintaining the lytic transcription program.