The preparation and characterization of relatively long (8 mm) cylindrical carbon fibre microelectrodes (CFMEs) modified with poly(3-methylthiophene) (P3MT) coatings is described, as well as their voltammetric behaviour in aqueous solutions. Electropolymerization was carried out by cyclic voltammetry in monomer acetonitrile solutions. Scanning electron micrographs showed that a very porous coating was deposited, producing a large increase in the modified electrode area. Such an increase led to loss of the diffusion characteristics typical of microelectrodes. Measurements of electroanalytical parameters of interest for a model system such as ferrocyanide in aqueous solutions were highly reproducible. The voltammetric behaviour of the phenolic antioxidant propylgallate (PG) in aqueous solutions at the modified electrode is reported. The effect of the different experimental variables involved in the P3MT electrosynthesis on the PG voltammetric signal has been considered. Under optimized conditions, no cleaning or pretreatment of the modified microelectrode was required over the whole working day. The PG oxidation process at a P3MT-coated CFME was characterized by cyclic voltammetry, and results were compared with those obtained at bare and P3MT-coated glassy carbon disk electrodes of conventional size. A detection limit of 4.0 x 10(-7) moll(-1) was obtained for the determination of PG by differential pulse voltammetry at the P3MT-coated CFME.