The cyclic voltammetric behaviors of empty nanotubes and toluene-filled nanotubes were described. When the nanotube films exposed to air for one night, a pair of redox waves was observed that is probably ascribed to the presence of oxygen-containing groups bound to the surface of the nanotubes. Toluene-filled nanotube film is demonstrated to catalyze the electrochemical response of biomolecules such as dopamine and epinephrine, while empty multi-wall carbon nanotube film shows no or less electrocatalytic behavior to these biomolecules. This suggests that filled nanotubes have some particular properties compared to empty multi-wall carbon nanotubes and the development of filled nanotubes is necessary. (C) 2003 Elsevier Ltd. All rights reserved.