The spin-wave dispersion relations for the [110] and [001] symmetry directions in ferromagnetic dysprosium metal (isotopically enriched 96.8% with 163 Dy) have been studied between 4.7° and 77°K. Throughout this temperature ' range the^ measured temperature dependence of the energy gap at zero wave vector (q = 0) is in fair agreement with that predicted theoretically for the frozen lattice model. However, the magnitude of the total planar anisotropy deduced from these gap measurements is larger by a factor of two than that obtained from macroscopic measurements. The increase o£ the magnon energies with decreasing temperature is much more pronounced at q = 0 than near the Brillouin zone boundaries. Thus the magnitude of the isotropic exchange interaction decreases substantially, about 25% in the [001] direction, between 77° and 4.7°K. Significant magnon-phonon interactions are observed, parti-? cularly in the [110] direction where the acoustic magnon branch is mixed with both the longitudinal and transverse acoustic phonon branches. The peak in the Fourier transform of the exchange interaction, J(q), which at 77°K occurs near the wave vector of the helical-magnetic structure of Dy just above T c , persists down to 4.7°K with shifts to smaller q as the temperature is decreased. At 77°K the optic and acoustic spin-wave branches are degenerate, to within 0.1 meV, at the K-symmetry point of the Brillouin zone. However at 4.7°K this degeneracy is lifted, with AE = 0.8 meV, thereby indicating the existence of a temperature dependent long-range anisotropic magnetic interaction in Dy.