Precise resistivity rho (Omega cm) and viscosity eta (10(-2) p) measurements for isobutyric acid-water (IBAW) critical mixtures with added K+ and Cl- ions have been performed in the Arrhenius temperature domain of the electrolyte. From the activation energy, the resistivity-viscosity relation reveals a fraction power character over the whole range of parameters investigated. To analyze our data we have used an exponential formula derived from the equivalent Arrhenius law: rho/T proportional to (eta/T)(R), where R = E-rho/E-eta is the ratio between the resistivity and viscosity activation energies. In the case of the pure system (IBAW), the value of R is in vicinity of 1, but when the salt is added, the ratio R shows dependence on the (K+, Cl-) concentrations: 0.6 < R < 1. The domain of the validity of R is in conformity with the theoretical prediction. The Coulombic interaction is the origin of the deviation. (c) 2006 Elsevier B.V. All rights reserved.