The modification of conducting polymer electrodes with antibodies (i.e. proteins) by means of electrochemical polymerization is a simple step that can be used to develop an immunological sensor. However, the electrochemical processes involved leading to the generation of analytical signals by the sensor have not been fully investigated. In this work, we report on the characterization of the interaction between an antigen, human serum albumin (HSA) and an antibody-immobilized polypyrrole electrode (such as anti-HSA) using cyclic voltammetry (CV) and impedance spectroscopy. This interaction was monitored using electrochemical impedance spectroscopy at three different potentials. The potentials correspond to the three redox states of the electroconducting polymer (i.e. reduced, doped and overoxidized states). Evidence from the CV experiments confirmed that there was a shift in the potential, which was found to be proportional to the concentration. Both the CV and the impedance experiments indicated that this potential-dependent shift could be attributed to antibody-antigen (Ab-Ag) binding.