The development of an amperometric sensor for the determination of reduced glutathione (GSH) is described. The sensor is based on tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) incorporated into the graphite powder/Nujol oil matrix. The electrooxidation of GSH was monitored amperometrically at 200 mV versus SCE (saturated calomel electrode). The amperometric response of the sensor was linearly proportional to the GSH concentration between 20 and 300 mumol l(-1), in 0.1 mol l(-1) phosphate buffer (pH 8.0), containing 0.1 mol l(-1) KCl and 0.5 mmol l(-1) Na(2)H(2)EDTA, as supporting electrolyte. The detection limit, considering signal/noise ratio equal three, was 4.2 mumol l(-1) for GSH and the repeatability obtained as relative standard deviation was of 5.1 % for a series of 10 successive measurements. (C) 2004 Elsevier B.V. All rights reserved.1003333340