A poly(3-methylthiophene) (P3MT)-modified glassy carbon electrode (GCE) has been prepared in undeaerated acetonitrile solution under ambient conditions. The electrochemical behavior of epinephrine was studied systematically at the P3MT-modified GCE using cyclic voltammetry. The results indicate that the number and height of redox peaks of epinephrine are strongly dependent on the pH value of the phosphate buffer solution (PBS). Three peaks, one irreversible oxidation peak and one pair of reversible redox peaks, can be observed in neutral PBS while only one pair of redox peaks appear in 0.5 M sulfuric acid solution. In pH 4.0 PBS, the oxidation of epinephrine gives one more cathodic peak than that reported in the literature; in other words, six peaks or three pairs of redox peaks can be obtained due to the oxidation of epinephrine and the following chemical reaction. The effects of other conditions on the oxidative behavior of epinephrine were examined and the oxidative mechanism of epinephrine at the P3MT-modified GCE was discussed. (C) 2004 Elsevier B.V. All rights reserved.