Abstract: Viscosity of small fluid samples is measured by coupling an ultrasonically energized shear transducer to a fluid sample through a polymeric coupling layer having a thickness and shear impedance such as to produce a zero total reflection coefficient at least at one particular viscosity. In general, the thickness will be slightly greater than one-quarter wavelength. The use of the coupling layer produces a large increase in sensitivity, eliminates the need for sophisticated and expensive electronic circuitry, and makes it possible to determine viscosity by very simple circuitry responsive to transducer current.