Free electrolyte was removed by ion exchange from monodisperse polystyrene latex. Non‐Newtonian viscosities were measured at volume fractions from 0.05 to 0.50, at various electrolyte concentrations. Electrolytes included HCl,K2SO4,MgSO4,Al2(SO)4)3,andTh(NO3)4.Deionized latices exhibited yield stressesτ0which decreased with the diminishing volume fraction and with increasing electrolyte concentration. The effect of added electrolyte upon the viscosity of a freshly mixed dispersion depended upon its equivalent concentration (normality) and was independent of the chemical nature or valence types of the ions. Limiting viscositiesη1at high shear rates were independent of electrolyte content. At intermediate electrolyte levels, variation of shear stress τ with shear rate γ̇ followed Casson's equationτ1/2=τ01/2+η11/2γ̇1/2.