FxCycle™ PI/RNase Staining Solution is used for flow cyotmetric analysis of DNA content in fixed cells. Propidium iodide (PI), a popular red-fluorescent stain, binds to DNA by intercalating between the bases with little or no sequence preference and with a stoichiometry of one dye per 4–5 base pairs of DNA. PI also binds to RNA, necessitating treatment with RNase to distinguish between RNA and DNA staining. This propidium iodide solution includes DNase-free RNase A and a permeablization reagent. It comes ready to use: simply add the staining solution to fixed cells, incubate, and acquire on a flow cytometer without washing.