The effect of static elastic strain on the thermal conductivity of germanium has been measured in the temperature interval 1.5°to 4.2°K. A large increase in thermal conductivity was produced by  or  tension in antimony-doped samples in which the scattering of phonons is primarily due to donors. The theory of scattering of phonons by donors predicts the sign and magnitude of the effect. Samples without strong donor scattering show small piezo-thermal conductivity effects. © 1962 The American Physical Society.