The high resolution potential of capillary electrophoresis (CE) makes CE techniques valuable for separations of selenium species. Further, inductively coupled plasma-mass spectrometry (ICP-MS) affords element-specific multielement detection, providing extremely low detection limits. The combination of CE with ICP-MS promises to become a powerful tool for metal speciation. Therefore, an on-line hyphenation of CE with ICP-MS, which was developed earlier (Michalke, B., Schramel, P., Fresenius' J. Anal. Chem. 1997, 257, 594-599), was modified and applied to selenium speciation. For this reason, capil- lary zone electrophoresis (CZE) methods were developed, providing the possibility to analyze six Se species of interest in one run: Se (IV), Se (VI), selenium carrying glutathione (GSSeSG), selenomethionine (SeM), selenocystine (SeC), and selenocystamine (SeCM). The final CE method used an alkaline background electrolyte (Na,CO,/NaOH) with separation differentiated from the detection step during hyphenation. This resulted in short separation times (10 min) and a subsequent detection step of 100s. The Se species were sufficiently separated from each other and appeared at 7 s (SeCM), 16s (Se (VI)), 22s (SeC), 27s (Se (IV)), 35s (SeM) and 56s (GSSeSG) during the detection step. Detection limits were calculated as 10 or 20 c1g Se/L for inorganic Se sDecies and 35-50 pg