High-speed zone electrophoresis in a fused-silica capillary is described. Elevated electric fields and short capillary lengths allow a mixture of fluorescein isothiocyanate (FITC) labeled amino acids to be separated in times as short as 1.5 s. Formation of the analyte zone at the head of the capillary is controlled by laser-induced photolysis of a tagging reagent. This gating procedure allows rapid and automated introduction of sample into the capillary. Ultimately, Joule heating of the buffer limits the speed and efficiency of the separation.