The selenium species in nutritional supplement tablets, based on selenized yeast, were separated by capillary zone electrophoresis using capillaries coated dynamically with poly(vinyl sulfonate) and detected by ICP-MS. Sample pre-treatment consisted of cold-water extraction by sonication and subsequent incubation of the cold-water extract with 6 M hydrochloric acid at 110 degreesC. The total selenium concentration in the cold-water extract was 3.5 mg L-1 and corresponded to 9% of the total selenium content of the tablets. More than 20 different selenium compounds were separated in the cold-water extract within 13 min. The efficiency of the system corresponded to 620 000 theoretical plates. When spiking the sample with available standards, co-migration was observed with selenomethionine and selenocystine-Se-methylselenocysteine-the latter species were not separated. When the cold-water extract was hydrolysed in hot hydrochloric acid, 45% of the selenium migrated within a single peak that co-migrated with selenomethionine. Other peaks co-migrated with trimethylselenonium, Se-methylselenomethionine, and selenocystine-Se-methylselenocysteine, respectively. The precision for the analysis of the aqueous extracts expressed as relative standard deviation (n = 3) on peak heights and areas was in the range 1.4-5.3%. Detection limits were better than 15 mug L-1, corresponding to absolute detection limits less than 250 fg