Three different azobenzene derivatives (azobenzene diazonium tetrafluoroborate, Fast Garnet GBC sulphate salt and Fast Black K salt) were covalently attached to glassy carbon (GC) electrodes by electrochemical grafting. The grafting of GC surfaces was controlled by varying the number of potential cycles during the modification procedures. The presence of azo groups on the modified electrode surfaces was confirmed by X-ray photoelectron spectroscopy. The electrochemical properties of the modified electrodes were characterised by cyclic voltammetry and the rotating disc electrode (RDE) technique using the Fe(CN)(6)(3-/4-) redox system. The blocking behaviour of aryl films towards oxygen reduction was studied by linear sweep voltammetry and the RDE method. The blocking action of the aryl-modified electrodes for ferricyanide reduction was significantly greater than for O-2 reduction. By estimating the parameter of relative blocking efficiency the best barrier properties were observed for azobenzene-modified GC electrodes. (C) 2012 Elsevier B.V. All rights reserved.