2',7'-Dichlorofluorescein diacetate is as a cell-permeable fluorogenic probe to quantify reactive oxygen species (ROS) and nitric oxide (NO). It is rapidly de-esterified in cells is oxidized to form fluorescent 2',7'-dichlorofluorescein. 2'7-Dichlorofluorescein displays excitation/emission spectra of 492/515 nm.