Abstract A cohesive 1–45 μm catalyst has been fluidized in a column 145 mm in ID. Unexpanded bed heights ranged between 90 and 300 mm. The column freeboard acted as a guide for the sound waves generated by a loudspeaker located opposite the fluidizing gas distributor. Varying the sound pressure level resulted in dramatic changes in the quality of fluidization. Large clusters originally present in beds fluidized without sound were broken up into subclusters. Homogeneous bubble-free fludization was obtained with appropriate acoustic fields. Minimum fluidization-velocity and terminal velocity of bed solids suggested that, under these conditions, subclusters were made of a few relatively coarse particles and a large number of finer particles. The break-up of clusters into subclusters occurred at contact points where the external (drag and inertial) forces induced by the acoustic field were larger than the internal (cohesive) van der Waals forces.