Electrocatalytic oxidation of ascorbate (vitamin C) at poly (N-methyl aniline) modified electrode has been studied and compared with that proceeding at polyaniline modified sensor. A sigmoid-shaped anodic current transient as a response to addition of ascorbate was found for polyaniline modified electrode in pH-neutral solution, whereas a 'normal-shaped' current transient was found to be characteristic for poly(N-methylaniline) modified electrode. Based on this, a hypothesis on the autocatalytic mechanism for electrochemical oxidation of ascorbate was confirmed. It has been shown that poly(N-methlaniline) modified electrode can be used as an amperometric ascorbate sensor, operating in slightly acidic or pH-neutral buffer solutions at a controlled potential of 0.1-0.5 V versus Ag/AgCl, and the dependencies of current response on ascorbate concentration, the thickness of a polymer layer, and operating potential have been analyzed. (c) 2007 Elsevier Ltd. All rights reserved.