Results are presented of studies conducted to relate internal friction measurements in U to allotropic transformations. It was found that several internal friction peaks occur in $alpha$-uranium whose magnitude changed drastically after annealing in the $beta$ phase. All of the allotropic transformations in uranium are diffusional in nature under slow heating and cooling conditions. Creep at regions of high stress concentration appears to be responsible for high temperature internal friction in $alpha$-uranium. The activation energy for grain boundary relaxation in $alpha$-uranium was found to be 65.1 +- 4 kcal/mole. Impurity atoms interfere with the basic mechanism for grain boundary relaxation resulting in a distribution in activation energies. A considerable distribution in ln tau$sub 0$ was also found which is a measure of the distribution in local order and in the Debye frequency around a grain boundary. (auth)