A method based on a modified version of pressure-mediated capillary electrophoresis (PreMCE) has been developed for the elimination of the chromatographic bias inherent in effective electrophoretic mobilities measured by capillary electrophoresis. This new five-band PreMCE method can be readily executed on most commercial capillary electrophoresis instruments. It yields not only precise but also accurate effective mobilities and electroosmotic flow rates, even when the analytes and electroosmotic flow markers are strongly retained on the coated fused-silica capillary wall.