This paper discusses some experimental techniques for the measurement of sound absorbing materials in the 2- to 10-kc range. The experimental technique discussed is that of decay time measurements of a reverberant chamber. Several different kinds of signals have been used—namely pulsed sine waves, pulsed noise, and an impulse signal generated by the discharge of an underwater spark. The spark source was found the most convenient to use. Though at present the measurements are not as precise as those obtained in air-filled reverberation chambers, the method does allow a quantitative comparison of underwater absorbing materials. All analysis of precision of the method will be given. Other methods for measuring absorption will be described briefly. (Sponsored by the Office of Naval Research, Code 411.)