Electrolysis of (dimethylformamide) (DMF) solutions containing tetraalkylammonium iodide salts and dissolved iodine in a two-compartment cell separated by a Nafion membrane results in transfer of solution volume between the two compartments. The pumping process was reversible and the rate, which ranged from 20 to 50 muL/min, was controlled by the cell current. The volume of solution pumped was significantly greater than what is predicted from the apparent molar volumes of the species involved in the electrolysis and from the charge passed. The additional volume is attributed to migration-assisted solvent flow across the membrane separator. Comparison of pumping results for a series of Nafion materials indicated that the solvent flow was related to the number of solvent molecules per ion-exchange site in the membrane. Pumping occurred with and against small external pressures up to 0.1 atm. Analysis of apparent molar ionic volumes indicates that the electrode reaction, I-3(-) + 2e(-) = 3I(-), contributes little to the observed volume change. Instead, the pumping is associated almost entirely with the apparent molar ionic volume of tetraalkylammonium ions and migration-assisted flow of DMF. (C) 2004 The Electrochemical Society.