Elastic wave attenuation in porous media is due in part to the relative motion of the liquid and the solid. Biot's theory expresses this component in terms of permeability, fluid viscosity, frequency, and the elastic constants of the material. Experiments were performed to measure attenuation in the frequency range f (sub 20,000 cps by a resonant bar method; attempts to measure attenuation at very high frequencies gave more equivocal results. Alundum bars were used to test the validity of the theory, for with these the loss not due to fluid motion is relatively small. Experiments were also made with natural specimens of rock. These showed that when not subjected to compacting pressure both the velocities and decrements of specimens were affected chemically and physically by the presence of liquid pore saturants. It is concluded that Biot's theory seems generally applicable to the determination of the fluid-solid or "sloshing" losses in resonated porous media. There is still some doubt about the applicability of the theory in the case of measurements made by pulse techniques. The use of attenuation measurements as a logging technique, possibly to estimate permeability, is also discussed.