A simple and effective amperometric biosensor based on PVC/TTF-TCNQ composite electrode is proposed for glucose determination. Glucose oxidase (GOx) was immobilized by crosslinking with glutaraldehyde. The TTF-TCNQ salt acts as a conducting phase and as a redox mediator, without needing the addition of any other substance. The biosensor can be applied in batch (response linear up to 5.0 mM, with a limit of detection, s/n = 3, of 8.5 x 10(-6) M) and in FIA systems (linear range between 0. 1 and 8.0 mM, with a limit of detection, s/n = 3, of 1.9 x 10(-5) M). It is also proposed a simple procedure that allows glucose and ascorbic acid to be simultaneously determined. (c) 2007 Elsevier B.V. All rights reserved.