The extensional viscosity characteristics of concentrated (45% w/w) latex dispersions containing various soluble polymers have been determined by using an opposing jet rheometer. In all cases, the latex dispersions were found to exhibit strain thinning behavior. Quantitative comparison with shear now data, through calculation of the Trouton ratio, indicated the extensional viscosities of the dispersions to be 1-2 orders of magnitude greater than their shear flow viscosity at a comparable deformation rate. For a given added polymer concentration, the latex dispersions containing cellulose ether type thickeners exhibited more pronounced shear and strain thinning characteristics and higher Trouton ratios than those dispersions thickened with associative polyelectrolytes. Mathematical modeling of the shear and extensional viscosities of the dispersions as a function of deformation rate has been undertaken by modification of the recent model of Barnes and Roberts.(1) The modified model was found to give an excellent fit of the shear viscosity data and a reasonably good fit of the extensional flow data over several decades of deformation rate.