The applicability of CZE with mass spectrometric detection for the determination of four chlorine species, namely chloride and three stable chlorine oxyanions, was studied. The main aspects of the proper selection of BGE and sheath liquid for the CE-MS determinations of anions with high mobility were demonstrated, pointing out the importance of pH and the mobility of the anion in the BGE. The possibility of using uncoated fused silica capillary and common electrolytes for the separation was shown and the advantage of using extra pressure at the inlet capillary end was also presented. The linear range was found to be 1-100 mu g/mL for ClO3- and ClO4-, 5-500 mu g/mL for ClO2-, and 25-500 mu g/mL for Cl-, but the sensitivity can be greatly improved if larger sample volume is injected and electrostacking effect is utilized. The LOD for ClO3- in drinking water was 6 ng/mL, when very large sample volume was injected (10 000 mbar center dot s was applied).