The viscosity virial coefficient characteristic of a moderately concentrated dispersion [and proportional to the Huggins coefficient] is calculated for electrostatically stabilized monodisperse suspensions of spherical colloid particles. The energy of interaction between two colloid particles is modeled as the sum of dispersion (van der Waals) and electric double-layer contributions. Comparisons of theoretical predictions and experimental data permit conclusions to be drawn about the adequacy of this model.