Abstract Propagation of ultrasonic shear waves at frequencies from 2.4 to 18 MHz was studies in three 18-carbon unsaturated fatty acid esters of cholesterol, cholesteryl obleate (CO), cholesteryl linoleacte (CL), and cholesteryl linolenate (CLn), and three mixtures of the esters, 80% CL-20% CO, 95% CL-5% CO, and 80% CLn-20% CO. The oleate and linoleate esters are of biological importance because they comprise about 70–80% of the cholesteryl esters contained in atherosclerotic plaque. A shear wave pulse superposition technique was used to obtain the complex shear mechanical impedance and, hence, the dynamic shear viscosity and dynamic shear rigidity. The reflectance technique permits the study of liquid crystals whose long axes are oriented, in the plane of shear, with respect to the shearing direction of the ultrasonic wave. Falling ball viscosity measurements using a Hoeppler precision viscosimeter were made as a function of temperature from 35 tc 55°C. Shear wave measurements of dynamic shear rigidity and dynamic shear viscosity are shown as functions of temperature. This work represents the first measurement of both the dynamic viscosity and rigidity in a liquid crystalline substance. In the smectic phase, a dynamic shear rigidity is exhibited in all systems studied. The shear mechanical impedance of cholesteryl linoleate is found to be independent or orientation of the long axis of the molecule with respect to the direction of shear in agreement with the prediction of Brochard which is based on Leslie's hydrodynamic theory of the cholesteric state. The dynamic shear viscosity is found to be dependent on the shear rate. This may be explained in terms of a relaxation in the short range order present in the isotropic phase of both nematic and cholesteric compounds, as recently discussed by De Gennes.