Quantitative measurement of GFP positive Huh-7 cells by flow cytometry after siRNA transfection. Huh-7 cells were co-transfected with HCVIRES-GFP plasmid with siRNA plasmid (pSuper-retro) by using the FuGENE 6 transfection reagent. After 48 hours of transfection, cells were harvested and GFP positive cells were analysed by a flow cytometer (Becton Dickinson, BD Biosciences, Clontech). Percentage of GFP-positive Huh-7 cells was quantitatively determined after siRNA transfection using cell quest computer software. The results were expressed as percentage of control. siRNA-74 was found to be most effective in silencing GFP from all IRES clones.