Elastic moduli of polycrystalline cadmium sulfide and polycrystalline magnesium fluoride have been obtained in a temperature range from 4.2 °K to 293°K. The results for both substances show that the temperature dependence of the elastic moduli can be very well described by an exponential equation . The polycrystalline isotropic elastic moduli are in excellent agreement with the values calculated from the corresponding single crystal constants using the Voigt -Reuss-Hill approximation.