A new pressure-mediated affinity capillary electrophoresis method for the rapid and accurate determination of drugprotein binding constants is described. A special combination of pressure and electrophoresis is used to shorten the electrophoresis and the overall analysis time to only a few minutes. At the same time, the suitability of this method is checked against a traditional fluorescence spectroscopy method. The binding constants of bovine serum albumin and a total of eight drugs with different pKa have been evaluated and compared with those determined by the fluorescence spectroscopy method and other methods in literature. The results indicate that the P-ACE method is well suited for the determination of binding constants with weak interaction (Kb<105?M-1).