Various matrix modifiers were investigated for the determination of molybdenum in human urine samples by electrothermal atomization atomic absorption spectrometry. Methods with nitric acid, barium difluoride, magnesium nitrate, palladium-magnesium nitrate and palladium-hydroxylamine hydrochloride were studied by introducing the urine samples directly into the graphite furnace with 0.3% Triton X-100. The charring and atomization curves, the amount of modifier and the calibration and addition graphs were studied in all instances. The precision, accuracy and chemical interferences of the methods were also investigated. The matrix interferences have been removed with the modifiers barium difluoride, palladium-magnesium nitrate and palladium-hydroxylamine hydrochloride. The limits of detection and quantification were 0.2 and 0.7 pg l-', respectively, for these modifiers. The characteristic masses were 14.1, 18.0 and 14.9 pg of MO for palladium-magnesium nitrate, palladium-hydroxylamine hydrochloride and barium difluoride, respectively. The method with palladium-magnesium nitrate has been applied to the study of the amount of molybdenum in human urine samples. The molybdenum levels found lie between 4.8-205.6 /*g 1-l.