The electrocatalytic reduction of dioxygen by anthra-9,10-quinone derivatives and dyes at polypyrrole modified glassy carbon electrodes has been investigated. The stability and electrochemical behaviour of the modified electrodes were examined at different pH media and pH 7.0 was chosen as the optimum working pH to study the electrocatalysis by comparing the shift in oxygen reduction potential and enhancement in peak current for oxygen reduction. Anthra-9,10-quinones combined with polypyrrole showed excellent electrocatalytic ability for the reduction of O-2 to H2O2 with overpotentials ranging from 320 to 665 mV in the anodic direction compared to bare glassy carbon electrode. The diffusion coefficient values of anthraquinones at the modified electrodes and the number of electrons involved in anthraquinone reduction were evaluated by chronoamperometric and chronocoulometric techniques, respectively. In addition, chronocoulometric and hydrodynamic voltammetric studies showed the involvement of two electrons in O-2 reduction. The mass specific activity of anthraquinones used, the diffusion coefficient of oxygen and the heterogeneous rate constants for the oxygen reduction at the surface of modified electrodes were also determined by rotating disk voltammetry. (c) 2005 Elsevier B.V. All rights reserved.