This paper presents a study of the transition of fluidization behaviour from Geldart Group B to A, through imposing a magnetic field on a fluidized bed of 0.141 m internal diameter. Iron particles of 330, 800 and 1600 mum in diameter were used as bed solids. The magnitude of the interparticle attractive force was varied by adjusting the electrical current through a pair of Helmholtz coils. The minimum fluidization and minimum bubbling velocities were obtained for various field intensities, enabling determination of the boundary between Group B and A behaviour. The characteristic interparticle forces at the B/A boundary were determined by establishing the relationship between interparticle force and the electrical current through the field coils. It was shown that the B/A transition occurred at the interparticle force to fluid drag ratio of about 2.5 for the three types of particles used. Analysis shows that these values are comparable with those for fine powders.