Direct redox conversion of microperoxidase-11 (MP-11) was demonstrated and studied by cyclic voltammetry on a gold electrode modified by a self-assembled monolayer (SAM) of 4,4’-dithiodipyridine (DTDP) or 1-octadecanethiol (ODT). The formation of the DTDP- and ODT-based SAMs on gold was evidenced by ellipsometry. The formal heterogeneous electron transfer rate constant of MP-11 redox conversion on the DTDP-modified electrode was 2.0(+/-0.3) X 10(-3) cm s(-1). The sigmoidal shape of the MP-11 voltammograms on the partly ODT-coated Au surface suggested the electron transfer at the monolayer-based microelectrode assemblies. Distinct mechanisms of the MP-11 redox conversion on the DTDP- and ODT-modified Au electrodes were discussed.