Ratios of limiting diffusion controlled currents recorded in aqueous solutions to those obtained in mixture with water-soluble organic co-solvents yield values of eta(rel)(1/2). These values can be used for evaluation of electrochemical experiments in such media and for distinguishing currents affected solely by a change in viscosity from those caused by other solvent-solute interactions, e.g. covalent additions. Limiting currents of Cd2+ ions and of 2-hydroxy-1,4-naphthoquinone proved to yield most reliable results, values of eta(rel)(1/2) obtained with Tl+ ions showed somewhat poorer correlation. The average values of eta(rel)(1/2) obtained from comparison of limiting currents for mixtures of water with ethanol and acetonitrile are in very good agreement with average values of tyres reported in the literature and in acceptable agreement for mixtures of water with 2-propanol. Nevertheless, the electrochemical data show much smaller standard deviations, than the data reported in the literature, which have shown inconsistencies when data from different sources are compared and can be considered as more reliable. The data obtained for mixtures of water with DMF have not been previously reported. (C) 2003 Elsevier Science B.V. All rights reserved.