Electrochemical impedance spectroscopy (EIS) was used to investigate the electrochemical behaviour of a gold electrode exposed to proteins prepared in phosphate buffer. Exposure to solutions of human serum albumin (HSA) and immunoglobulin G (Ig.G) resulted in a decrease of the double layer capacitance (C-dl) and an increase in the charge transfer resistance (R-ct) at the gold electrode solution interface. The greatest capacitance decrease for both proteins was observed when exposure occurred at or more positive to the electrode open circuit potential (OCP). Exposure to Ig.G resulted in a greater decrease in capacitance as compared to HSA under identical conditions. These capacitance and charge transfer resistance variations were attributed to the formation of a proteinaceous layer on the electrode surface during exposure. (C) 2004 Elsevier Ltd. All rights reserved.