The separation of four water-soluble vitamins, i.e., thiamine, riboflavine, pyridoxine and nicotinamide, was investigated by capillary zone electrophoresis and micellar electrokinetic chromatography. The usefulness of the internal standard technique in order to improve the precision of peak area when either the migration time or the injection volume varied was demonstrated. Quantitative analyses of different pharmaceutical formulations were compared with the LC method of the US Pharmacopeia. A good correlation was obtained.