The extensional viscosity characteristics of aqueous solutions of varying concentrations of three samples of hydroxyethylcellulose (HEC) of differing molecular masses have been determined using a commercially available opposed jet extensional rheometer. The results have been compared to the shear flow characteristics of the solutions and the Trouton ratio, T-R, of the various systems calculated. For all polymer solutions studied, T-R was found to approach the predicted Newtonian Value of 3 at low extensional strain rates. This observation was taken as a strong indication that the opposed jet rheometer was producing reliable extensional viscosity data. At higher strain rates, T-R generally increased with increasing strain rate and, for any given sample, with increasing polymer concentration thereafter. All HEC solutions studied were found to exhibit strain-thinning behavior in extensional now and shear-thinning behavior in shear flow, with the most pronounced effects being observed with the highest molecular mass sample (M(v) similar to 4.5 x 10(5) g/mol). The relative degrees of strain and shear thinning exhibited by the various HEC solutions have been quantified using the power law analysis. For the two samples of lowest molecular mass (M(v) similar to 6.5 x 10(4) and similar to 1.9 x 10(5) g/mol) the value of a power law index, n, in both extensional and shear now, was close to unity. For all solutions of the sample of highest molecular mass, the value of n in extensional flow was significantly higher than that observed in shear now. Regions of apparent strain thickening were observed for a few of the lowest viscosity solutions, but these observations were attributed to the onset of significant inertial effects rather than any coil-stretch transition phenomena.