A sensitive catalytic kinetic spectrophotometric method for determining ng ml−1concentrations of selenium is described. The method, based on the catalytic effect of Se (IV) on the reduction of azureA by sulphide, is monitored spectrophotometrically at 600 nm. The linearity range of the calibration graph is dependent on the concentration of sulphide. The variables affecting the rate of the reaction were investigated and the optimum conditions were established. The method is simple, rapid, precise, sensitive, free from many interferences and is widely applicable. The limit of detection is 2.5ng ml−1of Se. The relative standard deviation of seven determinations of 100 ng ml−1Se was 1.5%. The method was applied to the determination of selenium in spiked water, Kjeldahl tablets, synthetic samples and health care products.