HFF were grown in 24 well plates to 100% confluency in MEM with 10% FBS to establish viral inhibition of two low-passage clinical strains (BI-6 and CH19) via plaque assay. Cells infected with low-passage HCMV clinical strains (CH19 and BI6) do not release extracellular virus, but they display typical HCMV cytopathic effect (CPE). The percentage of infected cells was estimated visually in HFF monolayers. Dilutions of trypsinized cells were used as inocula for HFF monolayers in 24 well plates. After 7 days in culture, plaques were counted to determine the average number of plaques in 4-well replicates of each dilution. The optimal dilution for each virus strain produced an average of 60–80 plaques per well. CMVPT30-GFP having undergone multiple passages produces extracellular virus. Viral infection was quantitatively determined by PRA of culture supernatant medium. Cells were either exposed to GA for three hours prior to inoculation, or were inoculated prior to addition of medium containing GA at concentrations of 1, 2, 5, 10, and 20 µM in MEM with 1% FBS. One set of four wells was treated with DMSO as a vehicle control. For each experiment the remaining concentrations were represented in quadruplicate wells. Plates were read beginning at 7 days post inoculation (dpi) to determine the GA concentration producing a reduction of 50% in the number of plaques relative to vehicle control wells (IC50). Data were normalized to the vehicle controls, and probit analysis in SPSS was used to obtain 95% confidence intervals of the mean IC50 values.