To extend the application of a multichannel electrochemical detector (MED) for immunoassay, a MED system consisting of 8 sets of Pt electrodes in an arrangement fitted with the dimensions of a row of microtiter wells in a microtiter plate and a microcomputer-assisted 16-channel potentiostat was constructed. With this developed MED system, electroactive enzymatic products produced in eight microtiter wells can be analyzed simultaneously with a developed amperometric procedure. To demonstrate the applicability of the MED system for immunoassay, an immunosystem containing rabbit-IgG and alkaline phosphatase-conjugated goat anti rabbit-IgG was studied. From the dynamic range of 10-1000 ng/mL (0.064-6.4pM) and the detection limit of 1.0 ng/mL (6.4pM) obtained, the developed MED shows a tremendous improvement in sensitivity, detection limit, and efficiency compared with that obtained from conventional electrochemical immunoassay.