Carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) is a cell permeable dye generally used in animal cell proliferation research. High concentrations of the dye are toxic to animal cells, however concentrations in the region of 10 micromolar are typically sufficient to give strong staining with minimal cell death. CFDA-SE is often erroneously referred to as CFSE, even in scientific literature.