The electrocatalytic ability for oxygen reduction of a glassy carbon electrode modified with riboflavin and 9, 10-anthraquinones (AQNE) is investigated by cyclic voltammetry, chronoamperometry and chronocoulometry techniques. The stability of the modified electrodes is investigated in both acidic and neutral media. The influence of pH on the shift in the oxygen reduction potential and the enhancement in peak current leads to the selection of pH 7.0 as the optimum working value. Combined mediation of 9,10-anthraquinones and riboflavin results in overpotentials that are 592-729 mV lower than that for a plain glassy carbon electrode for reduction of O-2 to H2O2. The involvement of two electrons in oxygen reduction is confirmed from chronocoulometric and hydrodynamic voltammetric studies. The heterogeneous rate constants, mass specific current (MSC) and the diffusion coefficients are determined by rotating disc voltammetry. (c) 2005 Elsevier B.V. All rights reserved.