The experimental conditions for the indirect amperometric detection of Se(IV) by flow injection analysis have been optimized. The method is based on the Se(IV) reduction to Se(0) in acid medium in presence of an excess of iodide, being generated yotrion species which is electroactive and amperometrically detected at vitreous carbon electrode. The signal depends on the quantity of Se(IV) in the samples. Under optimized conditions, analytical conditions of the method were determined. The detection and quantification limits were 4.8 mu g l(-1) and 15.9 mu g l(-1), respectively. Because of the method proposed for its application to the determination of Se(IV) in natural water samples, it became necessary to increase the detection sensitivity and an on-line concentration stage was coupled. This stage is carried out on an anionic resin exchange (Dowex 1-X8). The detection and the quantification limits were in this case 0.06 mu g l(-1) and 0.2 mu g l(-1), respectively. The online preconcentration stage increases the sensibility of the amperometric detection which allows the Se(IV) determination at mu g l(-1) levels.