A kinetic-spectrophotometric method is presented for the determination of trace amounts of selenium (0.010 – 0.500 μ.ml−1), based on the catalytic effect of Se(IV) on the reduction of Gallocyanine by sodium sulfide, which yields a colorless product. The reaction is followed spectrophotometrically by measuring the absorbance change at 620 nm and 30 °C. The detection limit is 0.002 μ.ml−1. Se(VI) can be reduced with hot hydrochloric acid to Se(IV), allowing determination of total selenium. The variables which affected the reaction rate were fully investigated and the optimum conditions were established. The relative standard deviation for 50 ng.ml−1of selenium was 2.5% (n=6). The method was applied to determination of Se(IV) in real samples.