The electrochemical behavior of bovine erythrocyte superoxide dismutase (BESOD) on a hanging or dropping mercury electrode was studied by cyclic voltammetry (CV) and normal pulse polarography (NPP). Two defined peaks in CV or in NPP diagrams were attributed to the peaks of copper(II) and zinc(II), respectively. The electrode processes were irreversible and possessed an adsorptive characteristic. The adsorption of BESOD was estimated by double potential-step chronocoulometry. The average area of each molecule of absorbed BESOD was obtained, which is in good agreement with that determined by X-ray structure analysis. The diffusion coefficients were determined by NPP and double potential-step chronocoulometry, being in agreement with each other. The experimental results confirm that in the absence of a promotor or mediator, mercury electrodes are feasible for the investigation of BESOD. (C) 2004 Elsevier B.V. All rights reserved.