The bed behaviour of preliminarily fluidized beds has been investigated in the presence of an external magnetic field, using different ferromagnetic materials which are noncohesive in the absence of a magnetic field. The field was applied at fixed gas velocity on particles which are already fluidized. This mode of operation is known as 'magnetization LAST'. Homogeneous magnetic fields in two limiting orientations-axial and transverse-were used. The results are compared with those obtained when the field was applied to a static powder bed before fluidization, i.e. the 'magnetization FIRST' mode. The terms used to describe the regimes in both modes are reviewed.