Since 1980, when Plona observed slow wave propagation in water-saturated artificial rocks made of sintered glass beads, numerous attempts have been made to increase the sensitivity of his bulk wave techniques so that other materials of much smaller permeability (e.g., natural rocks) can be investigated also. Three of these experimental methods will be reviewed in this presentation. First, different ultrasonic interface waves propagating along a slightly corrugated fluid/fluid-saturation porous solid boundary are considered. Experimental results are presented to demonstrate the existence of Rayleigh- and Stonely (Scholte)-type leaky interface modes as well as a slow compressional skimming wave. Second, leaky Lamb modes propagating in a fluid-saturated porous plate are discussed. Both theoretical and experimental results indicate the existence of particular modes associated with slow wave propagation in the porous plate. Third, a novel technique based on the transmission of airborne ultrasound through air-filled porous plates was introduced. Experimental results on different artificial and natural materials show the presence of a strongly dispersive, highly attenuated, slow compressional wave predicted by Biot's theory. [This work was sponsored by the Department of Energy Basic Energy Sciences Grant No. DE-FG-02-87ER13749.A000.]