The ability of such a common redox mediator as 2,2'azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) to undergo sorption on carbon surfaces is explored here to convert multiwalled carbon nanotubes (CNTs) into a stable colloidal solution of ARTS-modified carbon nanostructures, the diameters of which are ∼10 nm (as determined by transmission electron microscopy). Subsequently, inks composed of fungal laccase (Cerrena unicolor) mixed with the dispersion of ABTS-modifled CNTs and stabilized with Naflon, were deposited on glassy carbon and successfully employed to the reduction of oxygen in Mcllvain buffer at pH 5.2. For comparison, the systems utilizing only ABTS-free CNTs and laccase as well as ARTS-modified CNTs did not show appreciable activity toward the oxygen reduction. The three-dimensionally distributed ABTS-modified CNTs are expected to improve the film's overall conductivity and to facilate electrical connection between the electrode and the enzyme. The network film of ABTS-modified CNTs is rigid, and it is characterized by charge propagation capabilities comparable to the conventional redox polymers. The whole concept of utilization of CNTs modified with ultrathin films of redox mediators in the preparation of efficient bioelectrocatalytic films seems to be of general importance to electroanalytical chemistry and to the development of biosensors. [ABSTRACT FROM AUTHOR]