The viscosity and electrical conductivity of aqueous solutions of trehalose and other saccharides containing 1:1 electrolytes have been measured. The decrease in the molar conductivity of each of these electrolytes with increasing viscosity is less than that predicted by Walden's rule. Instead, the empirical relation Lambda eta (alpha) = constant, which has already been found for other glass-forming liquids, holds for these mixtures, The microscopic origin of the deviation from the viscous friction model could be related to the presence of local heterogeneities in the distribution of water about the ions. This hypothesis is supported by the results of extensive molecular simulations. The temperature dependence of the Walden product of NaCl in aqueous trehalose mixtures indicates that this salt is fully dissociated close to the glass-transition temperature (T-g).