Capillary columns packed electrokinetically with 1.5-μm nonporous octadecylsilica particles are used to achieve rapid separations with high efficiencies. A mixture containing five polycyclic aromatic hydrocarbons (PAHs) as test compounds is separated in less than 5 s with 28 kV applied to a column with a packed length of 6.5 cm (10 cm total length). A sample containing 16 PAHs (classified as priority pollutants by the U.S. Environmental Protection Agency) is isocratically separated in under 10 min by using longer columns (15-30 cm). Separation efficiencies greater than 700 000 theoretical plates/m are obtained when detection (via UV-excited laser-induced fluorescence) is performed on the packed portion of the capillary. The outlet frit is observed to play an important role in determining column efficiency. The optimum flow rate for best separation efficiency occurs at ∼2 mm/s. The run-to-run reproducibility of the peak retention times on a single column is better than 1% (relative standard deviation).