Measured viscosity vs shear rate relationships were analyzed for a wide variety of carboxylated latexes reported in the literature using a modified effective-medium theory proposed by one of the authors. The theory contains three main parameters, c(m), k(o), and delta, which are the maximum volume fraction, a particle interaction parameter, closely related to the secondary electroviscous effect, and the thickness of the stabilizing surface layer, respectively. It is assumed that sheared dispersions always approach close packing for high volume fractions, i.e., c(m)=0.74 (for monodisperse suspensions). In general, k(o) increases with the magnitude of the secondary electroviscous effect and its value varies typically between 2.46 and 4.0 for low Peacuteclet numbers, Pe, and approaches 1.7 for very high Pe. For dispersions of highly charged particles at low electrolyte concentrations, the electroviscous effects become especially significant and experiments show that the viscosity can increase by more than three orders of magnitude when the electrolyte concentration is reduced from 10(-1) to 10(-3) M, an effect predicted by the modified effective medium theory. The viscosity of carboxylated latex is also influenced by a "hairy" surface layer, the thickness, delta, of which appears to be closely related to the amount and type of functional monomers, and the degree of dissociation of carboxylic acid groups on the latex surface. The theory also explains the shear thinning behavior of blends of latexes with different size.