We have measured the lattice thermal conductivity between 0.35 and 4°K of annealed, polycrystalline specimens of Cu-Ge alloys with residual resistivities between 10 and 22 μΩ cm. This is an extension of earlier work to lower temperatures and higher resistivities. Over most of the measurement range the phonons are primarily scattered by electrons, and the main features continue to be well described by Pippard's relations for the phonon-electron interaction. There is a marked size effect, showing that scattering by the external boundaries is effective up to 4°K. There is some evidence for additional scattering, but the uncertainties of the analysis do not allow a definite conclusion on this point. © 1966 The American Physical Society.