Adhesion forces between bovine serum albumin (BSA) immobilized on gold Substrate and an anti-BSA antibody conjugated on the gold coated probe of atomic force microscope (AFM) were determined by a force curve measurement. Specific adhesion forces were detected between the antibody-conjugated probe and immobilized BSA. The frequency of specific interactions was suppressed by adding free BSA. This result indicated that the curves originated from specific antigen-antibody interactions. On the basis of the above mentioned result, adhesion forces of an anti-Escherichia coli antibody known to recognize a protein located on the cell surface of E. coli were measured. E, coli cells were specifically detected by the measurement of adhesion forces between E. coli cells and the anti-E. coli antibody-conjugated probe. The AFM image of a single E. coli cell was also obtained using the anti-E. coli antibody-conjugated probe,