Dihydrofluorescein diacetate is a fluorimetric probe mainly used for oxidative stress measurements, in both cell-free systems and cellular models. In Vitro: Dihydrofluorescein diacetate may be a superior fluorescent probe for many cell-based studies. It is a better fluorescent probe for detecting intracellular oxidants because it is more reactive toward specific oxidizing species. Dihydrofluorescein diacetate demonstrates fluorescence of linear structures, consistent with mitochondria, in reoxygenated endothelium^[1]. Dihydrofluorescein diacetate is able to detect the presence of ROS in mitochondria. Dihydrofluorescein diacetate fluorescence was sharp and delineated thin filaments which corresponded in all details to TMRM-stained mitochondria. It enters mitochondria and reacts with ROS released in the matrix^[2]. Dihydrofluorescein diacetate could be an useful and quantitative method for measuring the oxidative potential of nanoparticle-treated cells^[3].