A design for an extensional viscometer is described which is useful for studying low‐viscosity fluids at high strain rates. The configuration consists of opposing nozzles through which the liquid is either sucked in or blown out. Measurement of the force required to keep the nozzles at a fixed distance apart as a function of flow rate directly yields a determination of the extensional viscosity. Data are presented on both Newtonian and non‐Newtonian liquids. For Newtonian liquids, Trouton's rule is verified for both uniaxial extensional and compressive flows. Results are also presented on dilute solutions of polyacrylamide and Xanthan gum which indicate substantial enhancements of the extensional viscosity upon addition of these polymers. Qualitative differences were observed, however, for the extensional flow behavior of the flexible polyacrylamide chains and the more rigid and rodlike Xanthan gum chains.