An electrode composed of glucose oxidase (GOD) immobilized in electropolymerized polyaniline (PANI) on a Pt wire of diameter 0.5 mm was prepared. Scanning tunneling micrographs of both PANI and GOD + PANI showed a wavy long-chain polymer structure, but the latter appeared smoother, thicker and well distributed. The dependences of the oxygen reduction current and the glucose-reduced GOD oxidation current on the glucose concentrations were found from cyclic voltammograms of a GOD + PANI + Pt electrode in glucose solutions. The compound 7-acetyl-10-methyl isoalloxazine (C13H10N4O3) was used as a model of the redox center on the GOD molecule. The results showed that at a potential of -0.3 V/SCE glucose-reduced GOD could be oxidized again and direct electron transfer could occur from the active redox center of the enzyme to the Pt surface through an electron pathway in GOD + PANI and its model electrodes.