Most authors have used the fluorescence of Se-DAN complex for the fluorimetric determination of Se in biological samples. A considerable variation of the analytical conditions of this fluorimetric determination has been observed. All the original Se-compounds in the sample must be converted to selenite. Therefore, a previous step of mineralization of samples and reduction to selenite is required for the fluorimetric determination. The conditions for the digestion of samples may be chosen as a function of the sample to be analyzed. Heating with HCl for a variable time is usually used in the reduction step. For the complete formation of Se-DAN complex and to obtain the maximum fluorescent signal, the pH must be adjusted to values between 1-3 and then heated for a variable time depending on the temperature chosen. Application of organic solvents, surfactants and cyclodextrins has been studied to increase the fluorescent intensity and improve the sensitivity of the fluorimetric determination in aqueous medium. It is necessary to improve analytical methods in order to obtain adequate information about speciation studies. There are other fluorimetric methods alternative to the use of Se-DAN complex such as the use of 2,3-diamino-1,4-dibromonaphthalene (Br2-DAN) to obtain the fluorophrore complex or the oxidation of non-fluorescent 2-(α-pyridyl)-thioquinaldinamide (PTQA) to a fluorescent compound in acidic medium by Se(IV).