The electroviscous effect of salt-free suspensions is analyzed theoretically. Our system is a colloidal suspensionthat has no ions different than those arising from the charge process of the spherical colloidal particles. Thetheory is based on a cell model for the particle−particle electrohydrodynamic interactions, and is valid forarbitrary surface charge density and particle concentrations. We study the influence on the electroviscouscoefficient of the surface charge density, the particle volume fraction and the drag coefficient and valence ofthe added counterions.