The method of phase comparison of continuous waves is applied to determine the dispersion relation, phase velocity, and group velocity as a function of frequency in dispersive materials. A combination of the variable frequency method and the variable path‐length method is found necessary to eliminate any uncertainty in the dispersion relation determination. Experiments are performed on specimens of various thicknesses. A constraint equation is derived from the assumption that the dispersion relation is unique and independent of the specimen thickness. This equation provides a procedure for determining the absolute number of wavelengths in the specimen. A transducer self‐compensation procedure is also used to reduce the errors in analyzing the test results among the specimens. Measurements in unidirectional, fiber‐reinforced Boron‐Epoxy specimens show good agreement with results reported previously in the literature. [Supported by AFOSR Grant 76‐299.2.]