Sharp peaks of Escherichia coli JM 109 (up to 1300 000 theoretical plates) were recorded with either extremely diluted (< 5 mm) or extremely concentrated (ca. 150 mm) Tris-borate (TB) running buffers. However, under the conditions of yielding sharp peaks, migration time of E coli was irreproducible. Critial factors influencing reproducibility were found to include bacterial growth phase, storage condition, cell pretreatment before injection, and concentration of running buffer. Buffer concentrations in the range of 20-100 mm TB were essential for reproducibility. E coli JM 109 was shown to be sensitive to ultrasonification. Bacterial growth and storage conditions could be monitored by CE, with results comparable to those obtained with optical methods.