The use of ultrasonic absorption measurements as a diagnostic tool for monitoring the particle size of coal-water slurries has been suggested by M. C. Davis [J. Acoust. Soc. Am. 65, 387 (1979)]. The present paper reports some experimental data obtained from ultrasonic absorption and velocity measurements on electrostatically and sterically stabilized coal-water slurries of average particle diameters of 5 and 50 μ. Ultrasonic absorption measurements were made in the frequency range of 1 to 25 MHz for 1 °C to 80 °C. The results are compared with various explicit expressions for heat conduction, viscous drag losses, and scattering of sound by particles. The experimental absorption was consistently higher than that predicted, even when allowing for the averaging effect era wide particle size distribution. The experimental results also indicate that velocity measurements in a coal-water slurry have the potential of becoming another possible diagnostic tool along with attenuation measurements. [Work partially supported by ONR.]