Phase comparison at high ultrasonic frequencies is found to be particularly suited to velocity of propagation measurements (and hence measurement of elastic constants) for small solid specimens such as single crystals. Both longitudinal and transverse waves may be used, with accurate results possible even when the specimen loss becomes high.A pulse technique is used which allows exact determination of the number of wave‐lengths in the acoustic path, and a direct measurement of phase shift at reflecting interfaces. The use of λ/4 plastic coupling seals to minimize errors is explained; necessary theoretical analysis is included.Illustrative data for fused silica and single crystal germanium are given.