This study evaluates ultrasound as a non-invasive technique for determining the cross-sectional holdups of multiphase systems. Experiments are performed in a column of 292 mm inner diameter with air, water and uniform glass beads of 1.3 mm diameter as the particles. In a bubble column, the signal intensity decayed exponentially with increasing gas holdup. In a liquid-solid fluidized bed, the wave time-of-flight decreased linearly when the solids holdup increased from 25% to 60% (fixed bed), while the signal intensity increased. Signal attenuation limits the use of this method for three-phase fluidized beds. When large particles (mm range) are used, it is difficult to operate at a wavelength that permits transmission through both dispersed phases. For three-phase systems, slurry bubble columns with low dispersed phases holdups and smaller particles present a less attenuative media and are better suited to this technique.