D-Fructose dehydrogenase (FDH) has been irreversibly adsorbed without loss of the enzymatic activity on Ketjen black (KB)-modified glassy carbon electrodes, although the adsorption rate is very slow probably owing to the microstructure of KB. The FDH-adsorbed electrode produced the enzyme- kinetic-controlled catalytic oxidation wave Of D-fructose at current densities of as high as 10mAcm(-2) without a mediator, in which the electron in FDH seems to be directly transferred to the electrode via the heme c site. No hindrance was observed in the mass transfer Of D-fructose to KB-modified electrodes.