The CellTrace™ CFSE Cell Proliferation Kit provides a versatile and well-retained cell-tracing reagent in convenient single-use vials. Carboxyfluorescein diacetate succinimidyl ester, often called CFSE, passively diffuses into cells. It is colorless and non-fluorescent until the acetate groups are removed by intracellular esterases to yield highly fluorescent carboxyfluorescein succinimidyl ester. The succinimidyl ester group reacts with intracellular amines, forming fluorescent conjugates that are well retained and can be fixed with aldehyde fixatives. The kit contains CFSE in ten single-use vials so that small-scale experiments can be performed without preparing excess quantities of perishable CFSE stock solution. The kit also includes high-quality DMSO (dimethylsulfoxide) and a detailed protocol.