BACKGROUND Vancomycin (VCM) has a bacteriostatic effect on gram-positive bacteria such as the methicillin-resistant Staphylococcus aureus. METHODS A new assay for measuring vancomycin concentration by micellar electrokinetic capillary chromatography using direct serum injection was developed. A borate buffer (pH 10.0) containing 100 mmol/l sodium dodecyl sulfate was used as an electrophoresis buffer, and the detection was at 210 nm. The migration time of vancomycin was approximately 7 min. RESULTS The linearity was from 0 to 100 microg/ml, with the limit of detection of 1.0 microg/ml (S/N=3). The within-run CV was 3.99-5.53%, and the recovery rate was 91-103% for a concentration range of 6.5-45.5 microg/ml. The between-day CV was 6.76% at 22.2 microg/ml. There was no interference from 32 other antibiotics. The correlation coefficient between the assay and fluorescence polarization immunoassay and direct injection HPLC was 0.982 and 0.985, respectively. The assay required no sample preparation of serum and used only microquantities of an electrophoresis buffer and samples. CONCLUSIONS This assay is cost-effective and suitable for routine clinical use.