Thermal Conductivity of Niobium in Magnetic Fields NearHc2

We report thermal-conductivity measurements on two samples of pure Nb in magnetic fields near ${\mathrm{H}}_{c2\mathrm{}}$. The measurements are in excellent agreement with the dependence on field, electron mean free path, and field orientation predicted by the recent theory of Houghton and Maki. The magnitude of the depression of the thermal conductivity in the mixed state is, however, about a factor of 2 less than predicted.