A simple and sensitive catalytic spectrophotometric method was developed for the determination of trace amounts of selenium. The method is based on the catalytic effect of selenium in form Se(IV) on the reduction of Maxilon Blue-SG by sodium sulfide. Indicator reaction is followed spectrophotometrically by measuring the absorbance change at lambda(max) = 654 nm and constant temperature (30.0+/-0.1 degreesC) by fixed time method. Selenium could quantitatively be determined in the range 0.004-0.200 mug ml(-1) Se(IV) with a detection limit of 0.205 ng ml(-1) Se(IV). All of the variables that affected the reaction rate were investigated and established optimum conditions to give maximum sensitivity. The R.S.D.s of the method (N = 12) for the Se(IV) concentrations of 0.004, 0.016, 0.040 and 0.160 mug ml(-1) are between 2.27 and 0.32%, respectively, and depended on Se(IV) concentration. The interference effect of various anion and cations on the Se(IV) determination was also fully studied. The selectivity of catalytic reaction was greatly improved with the use of the strong cation exchange resin. The developed kinetic-catalytic reaction was applied to the determination of selenium in real samples as Antioxidant-S, Selsun (which is a healthcare product for the treatment of dandruff) and analytical grade sodium metabisulfite, and in spring water samples without any pre-concentration. The acceptable recoveries were obtained by the method for appropriate standard Se(IV) additions. The method is simple, practical and suitable for using in small laboratories owing to its precision, sensitivity and relative selectivity. (C) 2003 Elsevier Science B.V. All rights reserved.