Electron transport catalyzed by a membrane-bound enzyme, D-fructose dehydrogenase (FDH), from one aqueous phase (W1) containing D-fructose to another one (W2) containing [Fe(CN)(6)](3-) across a planar bilayer lipid membrane (BLM) containing 7,7,8,8-tetracyanoquinodimethane (TCNQ) was investigated electrochemically. We found that the ion transport across the BLM was driven at the same time by the electromotive force generated by the electron transport.