An instrumental device for capillary electrochromatography (CEC) is described that permits conditioning of packed columns at pressures up to 100 bar, in or on-column fluorescence detection and electrokinetic sample injection. Capillaries with varying inner diameters (75, 100, 150 mu m) packed with octadecyl silica gel (3 mu m) are compared for efficiency and detection sensitivity. The influence of counter pressure on electroosmotic velocity and plate number is discussed.