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This paper describes a new selective detection method of microorganisms such as bacteria by using dielectrophoresis together with antigen-antibody reaction. The authors had proposed the dielectrophoretic impedance measurement (DEPIM) method, which realized fast and easy detection of biological cells suspended in aqueous medium. However, highly selective detection of bacteria according to their species or strain, was rather difficult by utilizing only the dielectric property variation according to the cell type. In this paper, the authors propose a selective bacteria detection method using DEPIM combined with antigen-antibody reaction, which is widely used in clinical diagnosis. Two kinds of combinations of DEPIM with immunoassay are tested. In one method, agglutination of bacteria is employed to increase dielectrophoretic force. The other method utilizes antibody molecules immobilized onto the microelectrode surface. It is experimentally confirmed that both methods can leave peculiar bacteria on the electrode surface after preliminary dielectrophoretic enrichment. Furthermore, agglutinated bacteria can be electrically detected by residual increase of the electrode conductance. These findings suggest that target bacteria may be selectively detected from mixture of various bacteria by the improved DEPIM technique.