The use of ultrahigh column temperatures, up to 110 degreesC, in micellar electrokinetic capillary chromatography was investigated. The number of plates generated per unit time increased from 0.22 to 12.8 plates/s for separations at 15 degreesC and 110 degreesC, respectively. Ultrahigh-temperature micellar electrokinetic capillary chromatography was used for the separation of cyclic undecapeptides (cyclosporins). A minimum resolution of 1.39 was calculated for a critical peak pair at 110 degreesC, which is more than a 50% increase over resolution generated at 40 degreesC. During a run time of more than 90 min at 110 degreesC and at pH 9.3, no sample degradation or solvent boiling was observed.