Abstract Parts of the dispersion relations for BeO have been measured. These relations are for waves moving in the [10 1 0] direction with their polarization vectors in the (0001) plane. The initial slopes of the measured acoustical branches agree with those obtained from ultrasonics. Branch intercepts at the zone centers of 84 meV (1.27 × 10 13 rad sec ) and possibly 5 meV (8 × 10 12 rad sec ) were found. The dispersion relations are correlated with infrared. Reststrahlen and “frequency spectra” measurements and proposed models.