A method for indirectly detecting horseradish peroxidase (HRP) was described by CE with electrochemical detection. Details of selection for optimum conditions were presented. The detection limit of free HRP was 1.09 x 10(-12) M or 0.94 zmol (S/N = 3). A novel CE-based liquid-phase binding noncompetitive enzyme immunoassay (CE-EIA) was developed. In this method, after the noncompetitive immunoreaction in liquid phase, the free enzyme (HRP)-labeled antibody (Ab*) and the bound enzyme-labeled complex (Ag-Ab*) were separated and then the system of HRP catalyzing H(2)O(2)/o-aminophenol (OAP) reaction was adopted. Prostate specific antigen (PSA), carcinoembryonic antigen (CEA), and human chorionic gonadotropin (HCG) in human serum samples were detected without any sample preparation, with the detection limits (S/N = 3) of 0.22, 0.17 and 0.30 ng/mL, respectively. This technique has been successfully applied to detect simultaneously PSA, CEA, and HCG in 12 min, upon adding these three antigens into human serum to simulate patient serum. It proves that the CE-EIA technique proposed could be developed into a sensitive and new method for simultaneous clinical assay of multianalytes.