A Kodak Ektapro Hs motion analyzer is applied to observe the ultrasonic effect on the mixing and breakage processes of agglomerated crystals suspended in ethanol. Mixing processes with stirring and with ultrasound are investigated by the dispersion of ink in the ethanol and by the motion of small crystals. The vessel is divided into several sections to investigate the local mixing process. Velocity variance is used to indicate the difference of turbulence when ultrasound and impeller stirring are applied respectively. The cavitation distribution in different sections is also recorded, and the effects on particles of different sizes are investigated. Observation of the breakage processes in different sections shows that both collisions between crystals and the vibration and implosion of cavitation bubbles contribute to the breakage process of agglomerated crystals. Finally, the effect of ultrasonic treatment is also compared with impeller stirring and with mechanical grinding. (c) 2006 Elsevier B.V. All rights reserved.